diff --git a/AGENTS.md b/AGENTS.md
index e904ffe..9f59f60 100644
--- a/AGENTS.md
+++ b/AGENTS.md
@@ -127,7 +127,7 @@ Ely GPUI Component. A component library for GPUI, in light and dark.
 - A file on its way is a `files::Transfer` drawn by one row in `files::transfer`: TransferQueue and DownloadManager share it, and its actions follow its state.
 - Paths with `/` between folders become a tree through `lists::Folder::of`, for `FileTree` and `files::ArchiveViewer` alike.
 - A folder's path over its entries is `lists::path_bar`, and its first order is `lists::listed`, folders first by name: DirectoryListing and FileExplorer share both, so every view shows one path and one order.
-- A file's icon comes from `primitives::file_icon`, one map from name to icon for every chapter; `files::FileIcon` draws it. What fits across a width comes from `layout::columns_for`, and `layout::fit` adds the inset that centers it.
+- A file's icon comes from `primitives::file_icon`, one map from name to icon for every chapter, under the owner's `primitives::IconTheme`, whose rules by name and extension come first; `files::FileIcon` draws it. What fits across a width comes from `layout::columns_for`, and `layout::fit` adds the inset that centers it.
 - Badges, tags and avatars live in `data_display`; forms and shell draw theirs from there, and `data_display` imports neither. A hue worn in a row, a label's or an event's, is `data_display::color_mark`, and `Palette::hue` gives the chart color by index. Avatars take square pictures. A tag is never wider than its container; a long label ends in an ellipsis beside its remove mark.
 - A picture drawn in code reaches gpui as a `RenderImage`. A host that replaces one frees the old through `App::drop_image`, or every frame stays in the sprite atlas (the gallery's model).
 - `img()` keeps loading state, and moves an animated picture's frames, only with an id. Content masks are rectangles, so rounded corners survive only when the image fills its box without cropping.
@@ -185,6 +185,8 @@ Ely GPUI Component. A component library for GPUI, in light and dark.
 - A choice that names a person leads with their initials through `forms::Choice::avatar`, in the list and in a Select's trigger alike (`project::AssigneePicker`).
 - `typography::Ellipsis` shapes its line with the text style's own run, so a strike or an underline set on its box shows (`lists::ListItem::struck`, a closed task's title).
 - Focus that must follow an item to another parent is taken by the owner and keyed by the item: a handle gpui makes for an element dies with its path (`project::KanbanBoard`, whose cards keep focus across columns).
+- The theme's `platform`, the system's to start, decides the window buttons Ely draws, the title bar's layout and key caps, `secondary` included (`typography::keys::keystroke`). A title bar whose buttons the OS draws follows the OS.
+- A pane the window's blur shows through is `shell::Vibrancy`, filled with the palette's `glass`, in a window opened `WindowBackgroundAppearance::Blurred`: vibrancy on macOS, acrylic on Windows. gpui 0.2.2 has no Mica.
 - The chart's hues go by `theme::HUE_NAMES`, for an event's color and a label's alike.
 - Text whose every character counts, encoded data and keys, goes through `typography::literal`: JetBrains Mono draws `==` and `->` as ligatures (`devtools::Encoder`).
 
diff --git a/examples/gallery/pages/shell/chrome.rs b/examples/gallery/pages/shell/chrome.rs
index c7386bb..0a65fa0 100644
--- a/examples/gallery/pages/shell/chrome.rs
+++ b/examples/gallery/pages/shell/chrome.rs
@@ -1,8 +1,8 @@
 use ely_gpui_component::{
     buttons::IconButton,
     primitives::IconName,
-    shell::{ControlsStyle, TitleBar, WindowControls, drag_region},
-    theme::{ActiveTheme, ControlSize, Elevation, Radius, TextSize},
+    shell::{TitleBar, WindowControls, drag_region},
+    theme::{ActiveTheme, ControlSize, Elevation, Platform, Radius, TextSize},
     typography::Caption,
 };
 use gpui::{App, Div, IntoElement, ParentElement, Styled, Window, div, px};
@@ -25,9 +25,9 @@ pub fn window_frame(width: f32, height: f32, cx: &App) -> Div {
         .shadow(theme.elevation(Elevation::Raised))
 }
 
-fn demo_bar(id: &'static str, style: ControlsStyle) -> TitleBar {
+fn demo_bar(id: &'static str, style: Platform) -> TitleBar {
     TitleBar::new(id)
-        .style(style)
+        .platform(style)
         .title("Ely — Projects")
         .on_close(|_, _| log::info!("gallery: demo close refused"))
         .child(IconButton::new((id, 1usize), IconName::PanelLeft).size(ControlSize::Sm))
@@ -36,9 +36,9 @@ fn demo_bar(id: &'static str, style: ControlsStyle) -> TitleBar {
 
 pub fn title_bar(cx: &App) -> impl IntoElement + use<> {
     let styles = [
-        ("tb-mac", ControlsStyle::Mac, "macOS"),
-        ("tb-windows", ControlsStyle::Windows, "Windows"),
-        ("tb-linux", ControlsStyle::Linux, "Linux"),
+        ("tb-mac", Platform::Mac, "macOS"),
+        ("tb-windows", Platform::Windows, "Windows"),
+        ("tb-linux", Platform::Linux, "Linux"),
     ];
     section(
         "TitleBar",
@@ -88,7 +88,7 @@ pub fn window_controls(cx: &App) -> impl IntoElement + use<> {
                 "Mac",
                 plate().child(
                     WindowControls::new("wc-mac")
-                        .style(ControlsStyle::Mac)
+                        .platform(Platform::Mac)
                         .on_close(|_, _| log::info!("gallery: demo close refused")),
                 ),
                 cx,
@@ -97,7 +97,7 @@ pub fn window_controls(cx: &App) -> impl IntoElement + use<> {
                 "Windows",
                 plate().px_0().child(
                     WindowControls::new("wc-windows")
-                        .style(ControlsStyle::Windows)
+                        .platform(Platform::Windows)
                         .on_close(|_, _| log::info!("gallery: demo close refused")),
                 ),
                 cx,
@@ -106,7 +106,7 @@ pub fn window_controls(cx: &App) -> impl IntoElement + use<> {
                 "Linux",
                 plate().child(
                     WindowControls::new("wc-linux")
-                        .style(ControlsStyle::Linux)
+                        .platform(Platform::Linux)
                         .on_close(|_, _| log::info!("gallery: demo close refused")),
                 ),
                 cx,
diff --git a/examples/gallery/pages/theme/mod.rs b/examples/gallery/pages/theme/mod.rs
index 2cccafa..fd8dee0 100644
--- a/examples/gallery/pages/theme/mod.rs
+++ b/examples/gallery/pages/theme/mod.rs
@@ -11,8 +11,10 @@ use gpui::{
 
 mod editing;
 mod importing;
+mod platform;
 
 use super::Page;
+use crate::script::Step;
 use crate::ui::{section, specimen, specimens};
 
 pub const PAGE: Page = Page {
@@ -21,7 +23,12 @@ pub const PAGE: Page = Page {
     title: "Theme",
     summary: "Tokens every component reads. Light and dark share one grammar.",
     render,
-    script: &[],
+    script: &[
+        Step::Click("frosted-open"),
+        Step::Wait(700),
+        Step::ShotWindow("frosted", "frosted-window"),
+        Step::CloseWindow("frosted"),
+    ],
 };
 
 fn render(window: &mut Window, cx: &mut App) -> AnyElement {
@@ -149,6 +156,7 @@ fn render(window: &mut Window, cx: &mut App) -> AnyElement {
         )
         .child(editing::editor(window, cx))
         .child(importing::importing(window, cx))
+        .child(platform::platform(window, cx))
         .into_any_element()
 }
 
diff --git a/examples/gallery/pages/theme/platform.rs b/examples/gallery/pages/theme/platform.rs
new file mode 100644
index 0000000..3652918
--- /dev/null
+++ b/examples/gallery/pages/theme/platform.rs
@@ -0,0 +1,192 @@
+use ely_gpui_component::{
+    buttons::{Button, SegmentedControl},
+    files::FileIcon,
+    forms::Switch,
+    primitives::{IconName, IconTheme},
+    shell::{Vibrancy, WindowControls},
+    theme::{ActiveTheme, Platform, Theme},
+    typography::{Kbd, KbdCombo},
+};
+use gpui::{
+    App, AppContext, Bounds, Context, IntoElement, ParentElement, Render, Styled, TitlebarOptions,
+    Window, WindowBackgroundAppearance, WindowBounds, WindowOptions, div, point, px, size,
+};
+
+use crate::{
+    probe::{Opened, probe},
+    ui::{change, keep, section, specimen, specimens},
+};
+
+const PLATFORMS: [(Platform, &str); 3] = [
+    (Platform::Mac, "macOS"),
+    (Platform::Windows, "Windows"),
+    (Platform::Linux, "Linux"),
+];
+
+/// Whether the demo's own icon rules are on.
+struct Owned(bool);
+
+pub fn platform(window: &mut Window, cx: &mut App) -> impl IntoElement + use<> {
+    section(
+        "Platform Style · IconThemeProvider · VibrancyBackground",
+        "The theme's platform decides window buttons and key caps, and starts as the system's. An icon theme lays an owner's rules over Ely's file icons. A frosted pane lets a blurred window's backdrop through; gpui 0.2.2 blurs as vibrancy on macOS and acrylic on Windows, and has no Mica.",
+        cx,
+    )
+    .child(
+        specimens()
+            .child(specimen("Platform", platforms(cx), cx))
+            .child(specimen("IconTheme", icons(window, cx), cx))
+            .child(specimen(
+                "Vibrancy",
+                probe(
+                    "frosted-open",
+                    Button::new("frosted-open", "Open a frosted window")
+                        .on_click(|_, _, cx| frosted(cx)),
+                ),
+                cx,
+            )),
+    )
+}
+
+fn platforms(cx: &App) -> impl IntoElement + use<> {
+    let shown = cx.theme().platform;
+    let label = PLATFORMS
+        .iter()
+        .find(|(platform, _)| *platform == shown)
+        .map(|(_, label)| *label)
+        .expect("a listed platform");
+    let control = PLATFORMS.iter().fold(
+        SegmentedControl::new("platform", label),
+        |control, (_, label)| control.segment(*label, *label, None),
+    );
+    div()
+        .w(px(320.))
+        .flex()
+        .flex_col()
+        .gap_4()
+        .child(control.on_change(|picked, _, cx| {
+            let (platform, _) = PLATFORMS
+                .iter()
+                .find(|(_, label)| *label == picked.as_ref())
+                .expect("a listed platform");
+            Theme::update(cx, |theme| theme.platform = *platform);
+        }))
+        .child(
+            div()
+                .flex()
+                .flex_wrap()
+                .items_center()
+                .justify_between()
+                .gap_3()
+                .child(WindowControls::new("platform-controls"))
+                .child(
+                    div()
+                        .flex()
+                        .items_center()
+                        .gap_3()
+                        .child(Kbd::new("secondary-s"))
+                        .child(KbdCombo::new("secondary-k secondary-s")),
+                ),
+        )
+}
+
+fn icons(window: &mut Window, cx: &mut App) -> impl IntoElement + use<> {
+    let owned = keep("icon-theme", || Owned(false), window, cx);
+    let on = owned.read(cx).0;
+    let muted = cx.theme().colors.fg_muted;
+    let rows = ["Cargo.toml", "README.md", "main.rs", "logo.svg"].map(|name| {
+        div()
+            .flex()
+            .items_center()
+            .gap_2()
+            .child(FileIcon::file(name))
+            .child(div().text_color(muted).child(name))
+    });
+    div()
+        .w(px(240.))
+        .flex()
+        .flex_col()
+        .gap_2()
+        .child(
+            Switch::new("icon-theme", on)
+                .label("The owner's icons")
+                .on_change(move |on, _, cx| {
+                    let theme = if on {
+                        IconTheme::default()
+                            .name("Cargo.toml", IconName::Package)
+                            .name("README.md", IconName::BookOpen)
+                            .extension("rs", IconName::Braces)
+                    } else {
+                        IconTheme::default()
+                    };
+                    theme.apply(cx);
+                    change(&owned, cx, |owned| owned.0 = on);
+                }),
+        )
+        .children(rows)
+}
+
+fn frosted(cx: &mut App) {
+    let options = WindowOptions {
+        window_bounds: Some(WindowBounds::Windowed(Bounds::centered(
+            None,
+            size(px(560.), px(340.)),
+            cx,
+        ))),
+        titlebar: Some(TitlebarOptions {
+            title: Some("Frosted".into()),
+            appears_transparent: true,
+            traffic_light_position: Some(point(px(16.0), px(18.0))),
+        }),
+        window_background: WindowBackgroundAppearance::Blurred,
+        ..Default::default()
+    };
+    let handle = cx
+        .open_window(options, |_, cx| cx.new(|_| Frosted))
+        .expect("the frosted window opens");
+    Opened::insert("frosted", handle.into(), cx);
+}
+
+/// A window whose sidebar lets the desktop through.
+struct Frosted;
+
+impl Render for Frosted {
+    fn render(&mut self, _: &mut Window, cx: &mut Context<Self>) -> impl IntoElement {
+        let theme = cx.theme();
+        let colors = &theme.colors;
+        div()
+            .size_full()
+            .flex()
+            .font_family(theme.font_family.clone())
+            .text_color(colors.fg)
+            .child(
+                Vibrancy::new()
+                    .w(px(180.))
+                    .h_full()
+                    .pt_12()
+                    .px_3()
+                    .flex()
+                    .flex_col()
+                    .gap_1()
+                    .children(
+                        ["Library", "Recents", "Shared"]
+                            .map(|name| div().px_2().py_1().child(name)),
+                    ),
+            )
+            .child(
+                div()
+                    .flex_1()
+                    .h_full()
+                    .p_6()
+                    .pt_12()
+                    .bg(colors.bg)
+                    .border_l_1()
+                    .border_color(colors.border)
+                    .min_w_0()
+                    .text_color(colors.fg_muted)
+                    .child(
+                        div().child("The sidebar lets the desktop through; this pane stays solid."),
+                    ),
+            )
+    }
+}
diff --git a/src/agent/changes.rs b/src/agent/changes.rs
index ced7ea0..0946f8a 100644
--- a/src/agent/changes.rs
+++ b/src/agent/changes.rs
@@ -150,7 +150,7 @@ impl RenderOnce for FileChangeCard {
                     })
                     .child(Disclosure::new((self.id.clone(), "chevron"), open).size(IconSize::Sm))
                     .child(
-                        Icon::new(file_icon(&self.change.path))
+                        Icon::new(file_icon(&self.change.path, cx))
                             .size(IconSize::Sm)
                             .color(colors.fg_muted),
                     )
diff --git a/src/buttons/button.rs b/src/buttons/button.rs
index a840ad5..7c90224 100644
--- a/src/buttons/button.rs
+++ b/src/buttons/button.rs
@@ -1,13 +1,13 @@
 use gpui::{
-    App, ClickEvent, ElementId, FocusHandle, FontWeight, Hsla, IntoElement, Keystroke, MouseButton,
+    App, ClickEvent, ElementId, FocusHandle, FontWeight, Hsla, IntoElement, MouseButton,
     RenderOnce, SharedString, Window, div, prelude::*, transparent_black,
 };
 
 use crate::{
     motion::Spinner,
     primitives::{FocusRing, Icon, IconName},
-    theme::{ActiveTheme, ControlSize, IconSize, Mix, Palette, Radius, TextSize},
-    typography::keys::{Platform, keystroke_labels},
+    theme::{ActiveTheme, ControlSize, IconSize, Mix, Palette, Platform, Radius, TextSize},
+    typography::keys::{keystroke, keystroke_labels},
 };
 
 pub(crate) type ClickHandler = Box<dyn Fn(&ClickEvent, &mut Window, &mut App) + 'static>;
@@ -112,11 +112,15 @@ pub(crate) enum Slot {
     Last,
 }
 
-/// A keystroke as the platform spells it: `⌘S`, or `Ctrl+S`.
-pub(crate) fn shortcut_text(stroke: &Keystroke) -> String {
-    let platform = Platform::current();
+/// Fails on a keystroke gpui cannot read, when a builder takes it.
+pub(crate) fn keystroke_of(source: &str) {
+    keystroke(source, Platform::current());
+}
+
+/// A keystroke in gpui key syntax as `platform` spells it: `⌘S`, or `Ctrl+S`.
+pub(crate) fn shortcut_text(source: &str, platform: Platform) -> String {
     let glue = if platform == Platform::Mac { "" } else { "+" };
-    keystroke_labels(stroke, platform).join(glue)
+    keystroke_labels(&keystroke(source, platform), platform).join(glue)
 }
 
 #[derive(IntoElement)]
@@ -125,7 +129,7 @@ pub struct Button {
     label: SharedString,
     icon: Option<IconName>,
     trailing_icon: Option<IconName>,
-    shortcut: Option<Keystroke>,
+    shortcut: Option<SharedString>,
     variant: ButtonVariant,
     size: ControlSize,
     disabled: bool,
@@ -181,9 +185,8 @@ impl Button {
 
     /// Shows the keystroke that also runs it, e.g. `"cmd-s"`. Panics on a bad keystroke.
     pub fn shortcut(mut self, keystroke: &str) -> Self {
-        let parsed = Keystroke::parse(keystroke)
-            .unwrap_or_else(|error| panic!("button shortcut {keystroke:?}: {error}"));
-        self.shortcut = Some(parsed);
+        keystroke_of(keystroke);
+        self.shortcut = Some(SharedString::from(keystroke.to_string()));
         self
     }
 
@@ -226,7 +229,8 @@ impl RenderOnce for Button {
         let link = self.variant == ButtonVariant::Link;
         let icon = |name| Icon::new(name).size(icon_size).color(tone.fg);
         let radius = theme.radius(Radius::Md);
-        let hint = self.shortcut.as_ref().map(shortcut_text);
+        let platform = cx.theme().platform;
+        let hint = self.shortcut.map(|source| shortcut_text(&source, platform));
         let spinner = (self.id.clone(), "spinner");
         let parts = div()
             .flex()
diff --git a/src/buttons/quick.rs b/src/buttons/quick.rs
index 49f2361..f365138 100644
--- a/src/buttons/quick.rs
+++ b/src/buttons/quick.rs
@@ -1,11 +1,11 @@
 use std::rc::Rc;
 
 use gpui::{
-    App, ElementId, Entity, FontWeight, InteractiveElement, IntoElement, Keystroke, ParentElement,
-    RenderOnce, SharedString, StatefulInteractiveElement, Styled, Window, div, prelude::*,
+    App, ElementId, Entity, FontWeight, InteractiveElement, IntoElement, ParentElement, RenderOnce,
+    SharedString, StatefulInteractiveElement, Styled, Window, div, prelude::*,
 };
 
-use super::button::shortcut_text;
+use super::button::{keystroke_of, shortcut_text};
 use crate::{
     primitives::{FocusRing, Icon, IconName},
     theme::{ActiveTheme, ControlSize, IconSize, Radius, TextSize},
@@ -19,7 +19,7 @@ pub struct QuickAction {
     icon: IconName,
     label: SharedString,
     note: Option<SharedString>,
-    shortcut: Option<Keystroke>,
+    shortcut: Option<SharedString>,
     run: Run,
 }
 
@@ -45,9 +45,8 @@ impl QuickAction {
 
     /// Panics on a bad keystroke.
     pub fn shortcut(mut self, keystroke: &str) -> Self {
-        let parsed = Keystroke::parse(keystroke)
-            .unwrap_or_else(|error| panic!("quick action shortcut {keystroke:?}: {error}"));
-        self.shortcut = Some(parsed);
+        keystroke_of(keystroke);
+        self.shortcut = Some(SharedString::from(keystroke.to_string()));
         self
     }
 }
@@ -171,7 +170,7 @@ impl RenderOnce for QuickActions {
                             div()
                                 .text_size(theme.text_size(TextSize::Xs))
                                 .text_color(colors.fg_subtle)
-                                .child(shortcut_text(stroke)),
+                                .child(shortcut_text(stroke, theme.platform)),
                         )
                     })
             })
diff --git a/src/chat/attach.rs b/src/chat/attach.rs
index 43cbe75..d4b9aa2 100644
--- a/src/chat/attach.rs
+++ b/src/chat/attach.rs
@@ -80,7 +80,7 @@ impl RenderOnce for AttachmentChip {
                 .rounded(theme.radius(Radius::Sm))
                 .bg(colors.hover)
                 .child(
-                    Icon::new(file_icon(&item.name))
+                    Icon::new(file_icon(&item.name, cx))
                         .size(IconSize::Md)
                         .color(colors.fg_muted),
                 ),
diff --git a/src/chat/media.rs b/src/chat/media.rs
index 31fe0a5..66b1111 100644
--- a/src/chat/media.rs
+++ b/src/chat/media.rs
@@ -255,7 +255,7 @@ impl RenderOnce for FileMessage {
                     .rounded(theme.radius(Radius::Sm))
                     .bg(colors.hover)
                     .child(
-                        Icon::new(file_icon(&self.name))
+                        Icon::new(file_icon(&self.name, cx))
                             .size(IconSize::Md)
                             .color(colors.fg_muted),
                     ),
diff --git a/src/chat/projects.rs b/src/chat/projects.rs
index 53b2958..dd0be47 100644
--- a/src/chat/projects.rs
+++ b/src/chat/projects.rs
@@ -211,7 +211,7 @@ impl RenderOnce for ProjectKnowledgePanel {
                                     .py_1()
                                     .text_size(theme.text_size(TextSize::Sm))
                                     .child(
-                                        Icon::new(file_icon(&name))
+                                        Icon::new(file_icon(&name, cx))
                                             .size(IconSize::Sm)
                                             .color(colors.fg_muted),
                                     )
diff --git a/src/debug/session.rs b/src/debug/session.rs
index d56016b..85e5208 100644
--- a/src/debug/session.rs
+++ b/src/debug/session.rs
@@ -1,9 +1,8 @@
 use std::rc::Rc;
 
 use gpui::{
-    AnyElement, App, ElementId, FontWeight, InteractiveElement, IntoElement, Keystroke,
-    ParentElement, RenderOnce, SharedString, StatefulInteractiveElement, Styled, Window, div,
-    prelude::*,
+    AnyElement, App, ElementId, FontWeight, InteractiveElement, IntoElement, ParentElement,
+    RenderOnce, SharedString, StatefulInteractiveElement, Styled, Window, div, prelude::*,
 };
 
 use super::OnIndex;
@@ -68,14 +67,14 @@ impl RenderOnce for DebugToolbar {
         let theme = cx.theme();
         let colors = theme.colors.clone();
         let paused = self.state == DebugState::Paused;
+        let platform = theme.platform;
         let button =
             |command: DebugCommand, icon: IconName, words: &str, key: &str, enabled: bool| {
                 let run = self.on_command.clone();
-                let key = Keystroke::parse(key).expect("a debug key parses");
                 IconButton::new((self.id.clone(), format!("{command:?}")), icon)
                     .variant(ButtonVariant::Ghost)
                     .size(ControlSize::Sm)
-                    .tooltip(format!("{words}  {}", shortcut_text(&key)))
+                    .tooltip(format!("{words}  {}", shortcut_text(key, platform)))
                     .disabled(!enabled)
                     .when_some(run, |button, run| {
                         button.on_click(move |_, window, cx| {
diff --git a/src/documents/rich.rs b/src/documents/rich.rs
index dce1e25..1c82c67 100644
--- a/src/documents/rich.rs
+++ b/src/documents/rich.rs
@@ -98,6 +98,7 @@ impl RenderOnce for RichTextEditor {
         };
         let (open_link, close_link) = (set_linking(true), set_linking(false));
         let float_id: ElementId = (self.id.clone(), "float").into();
+        let platform = cx.theme().platform;
         let floating = FloatingToolbar::new(float_id.clone(), &self.field).children(
             INLINE.iter().map(|tool_of| {
                 let on = pressed.contains(&tool_of.0);
@@ -107,6 +108,7 @@ impl RenderOnce for RichTextEditor {
                     *tool_of,
                     on,
                     Some(open_link.clone()),
+                    platform,
                 )
             }),
         );
diff --git a/src/documents/toolbar.rs b/src/documents/toolbar.rs
index 2e9e98b..28e768c 100644
--- a/src/documents/toolbar.rs
+++ b/src/documents/toolbar.rs
@@ -1,4 +1,4 @@
-use gpui::{App, ElementId, Entity, IntoElement, Keystroke, ParentElement, RenderOnce, Window};
+use gpui::{App, ElementId, Entity, IntoElement, ParentElement, RenderOnce, Window};
 
 use super::format::{Format, active, format};
 use crate::{
@@ -6,7 +6,7 @@ use crate::{
     forms::{Run, TextInput},
     primitives::IconName,
     shell::{Toolbar, ToolbarGroup, ToolbarSeparator},
-    theme::ControlSize,
+    theme::{ActiveTheme, ControlSize, Platform},
 };
 
 /// A tool: the format it applies, its icon, its name and its key.
@@ -56,12 +56,10 @@ pub(crate) fn tool(
     (format_of, icon, name, key): Tool,
     on: bool,
     on_link: Option<Run>,
+    platform: Platform,
 ) -> ToggleButton {
     let tip = match key {
-        Some(key) => {
-            let stroke = Keystroke::parse(key).expect("a tool's key parses");
-            format!("{name}  {}", shortcut_text(&stroke))
-        }
+        Some(key) => format!("{name}  {}", shortcut_text(key, platform)),
         None => name.to_string(),
     };
     let field = field.clone();
@@ -105,10 +103,18 @@ impl RenderOnce for FixedFormatToolbar {
     fn render(self, _: &mut Window, cx: &mut App) -> impl IntoElement {
         let input = self.field.read(cx);
         let pressed = active(input.text(), input.selection());
+        let platform = cx.theme().platform;
         let group = |tools: &[Tool]| {
             ToolbarGroup::new().children(tools.iter().map(|tool_of| {
                 let on = pressed.contains(&tool_of.0);
-                tool(&self.id, &self.field, *tool_of, on, self.on_link.clone())
+                tool(
+                    &self.id,
+                    &self.field,
+                    *tool_of,
+                    on,
+                    self.on_link.clone(),
+                    platform,
+                )
             }))
         };
         Toolbar::new()
diff --git a/src/files/archive.rs b/src/files/archive.rs
index 623340c..a3674a2 100644
--- a/src/files/archive.rs
+++ b/src/files/archive.rs
@@ -8,7 +8,7 @@ use gpui::{
 use super::FileIcon;
 use crate::{
     lists::{Folder, Tree, TreeNode},
-    primitives::{IconName, file_icon},
+    primitives::{IconName, IconTheme, icon_theme},
     theme::{ActiveTheme, IconSize, TextSize},
     typography::{MiddleEllipsis, format},
 };
@@ -32,14 +32,19 @@ pub(crate) fn saving(size: u64, packed: u64) -> u64 {
 }
 
 /// Nodes for `folder` under `prefix`, folders first, then files, each by name; and the bytes it holds.
-fn nodes(folder: &Folder, prefix: &str, entries: &[ArchiveEntry]) -> (Vec<TreeNode>, u64) {
+fn nodes(
+    folder: &Folder,
+    prefix: &str,
+    entries: &[ArchiveEntry],
+    icons: &IconTheme,
+) -> (Vec<TreeNode>, u64) {
     let mut out = Vec::new();
     let mut held = 0;
     let mut folders: Vec<_> = folder.folders.iter().collect();
     folders.sort_by_key(|(name, _)| name.to_lowercase());
     for (name, inner) in folders {
         let path = format!("{prefix}{name}");
-        let (children, bytes) = nodes(inner, &format!("{path}/"), entries);
+        let (children, bytes) = nodes(inner, &format!("{path}/"), entries, icons);
         held += bytes;
         let node = TreeNode::new(path, name.clone())
             .icon(IconName::Folder)
@@ -63,7 +68,7 @@ fn nodes(folder: &Folder, prefix: &str, entries: &[ArchiveEntry]) -> (Vec<TreeNo
         );
         out.push(
             TreeNode::new(path, name.clone())
-                .icon(file_icon(name))
+                .icon(icons.file(name))
                 .note(note),
         );
     }
@@ -115,7 +120,7 @@ impl RenderOnce for ArchiveViewer {
         let theme = cx.theme();
         let colors = &theme.colors;
         let folders = Folder::of(self.entries.iter().map(|entry| entry.path.as_ref()));
-        let (nodes, size) = nodes(&folders, "", &self.entries);
+        let (nodes, size) = nodes(&folders, "", &self.entries, icon_theme(cx));
         let packed: u64 = self.entries.iter().map(|entry| entry.packed).sum();
         let top: Vec<SharedString> = folders
             .folders
diff --git a/src/files/icon.rs b/src/files/icon.rs
index 0126f03..7cd187b 100644
--- a/src/files/icon.rs
+++ b/src/files/icon.rs
@@ -1,4 +1,4 @@
-use gpui::{App, IntoElement, RenderOnce, Window};
+use gpui::{App, IntoElement, RenderOnce, SharedString, Window};
 
 use crate::{
     lists::DirEntry,
@@ -6,28 +6,34 @@ use crate::{
     theme::{ActiveTheme, IconSize},
 };
 
-/// A file's icon by its name's extension, or a folder's, open or shut.
+/// A file's name, its icon found under the icon theme at render, or an icon itself.
+enum Shown {
+    File(SharedString),
+    Icon(IconName),
+}
+
+/// A file's icon by its name under the owner's icon theme, or a folder's, open or shut.
 #[derive(IntoElement)]
 pub struct FileIcon {
-    icon: IconName,
+    shown: Shown,
     size: IconSize,
 }
 
 impl FileIcon {
     pub fn file(name: impl AsRef<str>) -> Self {
         Self {
-            icon: file_icon(name.as_ref()),
+            shown: Shown::File(name.as_ref().to_string().into()),
             size: IconSize::Md,
         }
     }
 
     pub fn folder(open: bool) -> Self {
         Self {
-            icon: if open {
+            shown: Shown::Icon(if open {
                 IconName::FolderOpen
             } else {
                 IconName::Folder
-            },
+            }),
             size: IconSize::Md,
         }
     }
@@ -48,7 +54,11 @@ impl FileIcon {
 
 impl RenderOnce for FileIcon {
     fn render(self, _: &mut Window, cx: &mut App) -> impl IntoElement {
-        Icon::new(self.icon)
+        let icon = match self.shown {
+            Shown::File(name) => file_icon(&name, cx),
+            Shown::Icon(icon) => icon,
+        };
+        Icon::new(icon)
             .size(self.size)
             .color(cx.theme().colors.fg_muted)
     }
diff --git a/src/lists/directory.rs b/src/lists/directory.rs
index 959acb9..a06fff6 100644
--- a/src/lists/directory.rs
+++ b/src/lists/directory.rs
@@ -296,7 +296,7 @@ impl RenderOnce for DirectoryListing {
                             Icon::new(if entry.is_folder() {
                                 IconName::Folder
                             } else {
-                                file_icon(&entry.name)
+                                file_icon(&entry.name, cx)
                             })
                             .size(IconSize::Md)
                             .color(colors.fg_muted),
diff --git a/src/lists/files.rs b/src/lists/files.rs
index f5656d1..39652a0 100644
--- a/src/lists/files.rs
+++ b/src/lists/files.rs
@@ -9,7 +9,7 @@ use super::{Tree, TreeNode};
 use crate::{
     data_display::Tone,
     forms::{SearchInput, TextInput},
-    primitives::{IconName, file_icon},
+    primitives::{IconName, IconTheme, icon_theme},
     theme::ControlSize,
 };
 
@@ -90,6 +90,7 @@ fn nodes(
     paths: &[SharedString],
     status: &[(SharedString, GitStatus)],
     query: &str,
+    icons: &IconTheme,
 ) -> (Vec<TreeNode>, Vec<SharedString>) {
     let root = Folder::of(paths.iter().map(|path| path.as_ref()));
     let state = |path: &str| {
@@ -104,6 +105,7 @@ fn nodes(
         query: &str,
         state: &dyn Fn(&str) -> Option<GitStatus>,
         open: &mut Vec<SharedString>,
+        icons: &IconTheme,
     ) -> (Vec<TreeNode>, bool) {
         let mut out = Vec::new();
         let mut changed = false;
@@ -111,7 +113,8 @@ fn nodes(
         folders.sort_by_key(|(name, _)| name.to_lowercase());
         for (name, inner) in folders {
             let path = format!("{prefix}{name}");
-            let (children, inner_changed) = walk(inner, &format!("{path}/"), query, state, open);
+            let (children, inner_changed) =
+                walk(inner, &format!("{path}/"), query, state, open, icons);
             if children.is_empty() && !matches(name, query) {
                 continue;
             }
@@ -136,7 +139,7 @@ fn nodes(
         files.sort_by_key(|name| name.to_lowercase());
         for name in files {
             let path = format!("{prefix}{name}");
-            let node = TreeNode::new(path.clone(), name.clone()).icon(file_icon(name));
+            let node = TreeNode::new(path.clone(), name.clone()).icon(icons.file(name));
             out.push(match state(&path) {
                 Some(state) => {
                     changed = true;
@@ -148,7 +151,7 @@ fn nodes(
         (out, changed)
     }
     let mut open = Vec::new();
-    let (nodes, _) = walk(&root, "", query, &state, &mut open);
+    let (nodes, _) = walk(&root, "", query, &state, &mut open, icons);
     (nodes, open)
 }
 
@@ -208,7 +211,7 @@ impl RenderOnce for FileTree {
             Vec::<SharedString>::new()
         });
         let query = filter.read(cx).text().trim().to_string();
-        let (nodes, open) = nodes(&self.paths, &self.status, &query);
+        let (nodes, open) = nodes(&self.paths, &self.status, &query, icon_theme(cx));
         let top: Vec<SharedString> = nodes
             .iter()
             .filter(|node| node.opens())
@@ -245,7 +248,7 @@ impl RenderOnce for FileTree {
 mod tests {
     use gpui::SharedString;
 
-    use super::{GitStatus, nodes};
+    use super::{GitStatus, IconTheme, nodes};
     use crate::lists::tree::{Shown, rows};
 
     fn paths() -> Vec<SharedString> {
@@ -267,7 +270,7 @@ mod tests {
             ("src/ui/Button.rs".into(), GitStatus::Modified),
             ("README.md".into(), GitStatus::Added),
         ];
-        let (nodes, open) = nodes(&paths(), &status, query);
+        let (nodes, open) = nodes(&paths(), &status, query, &IconTheme::default());
         let every = ["assets", "src", "src/ui"]
             .map(SharedString::from)
             .into_iter()
diff --git a/src/primitives/files.rs b/src/primitives/files.rs
index 6e20faf..54b2fad 100644
--- a/src/primitives/files.rs
+++ b/src/primitives/files.rs
@@ -1,9 +1,68 @@
+use std::{collections::HashMap, sync::LazyLock};
+
+use gpui::{App, Global};
+
 use super::IconName;
 
-/// The icon a file's name suggests, by its extension.
-pub(crate) fn file_icon(name: &str) -> IconName {
-    let extension = name.rsplit_once('.').map(|(_, ext)| ext.to_lowercase());
-    match extension.as_deref() {
+/// Which icon a file shows: an owner's rules by name and by extension, laid over Ely's map. Without one, Ely's map alone.
+#[derive(Clone, Default)]
+pub struct IconTheme {
+    names: HashMap<String, IconName>,
+    extensions: HashMap<String, IconName>,
+}
+
+impl Global for IconTheme {}
+
+impl IconTheme {
+    /// A file of this exact name, in any case: `Cargo.toml`, `Dockerfile`.
+    pub fn name(mut self, name: &str, icon: IconName) -> Self {
+        self.names.insert(name.to_lowercase(), icon);
+        self
+    }
+
+    /// Files ending in this extension, given without its dot.
+    pub fn extension(mut self, extension: &str, icon: IconName) -> Self {
+        self.extensions.insert(extension.to_lowercase(), icon);
+        self
+    }
+
+    /// Serves every window from now on.
+    pub fn apply(self, cx: &mut App) {
+        log::info!(
+            "icon theme: {} names, {} extensions",
+            self.names.len(),
+            self.extensions.len()
+        );
+        cx.set_global(self);
+        cx.refresh_windows();
+    }
+
+    pub(crate) fn file(&self, name: &str) -> IconName {
+        let name = name.to_lowercase();
+        let extension = name.rsplit_once('.').map(|(_, extension)| extension);
+        self.names
+            .get(&name)
+            .or_else(|| extension.and_then(|extension| self.extensions.get(extension)))
+            .copied()
+            .unwrap_or_else(|| ely_icon(extension))
+    }
+}
+
+static ELY: LazyLock<IconTheme> = LazyLock::new(IconTheme::default);
+
+/// The owner's icon theme, or Ely's map alone.
+pub(crate) fn icon_theme(cx: &App) -> &IconTheme {
+    cx.try_global::<IconTheme>().unwrap_or(&ELY)
+}
+
+/// The icon a file's name suggests, under the owner's icon theme.
+pub(crate) fn file_icon(name: &str, cx: &App) -> IconName {
+    icon_theme(cx).file(name)
+}
+
+/// Ely's icon for a file by its extension, in lower case.
+fn ely_icon(extension: Option<&str>) -> IconName {
+    match extension {
         Some(
             "rs" | "ts" | "tsx" | "js" | "jsx" | "py" | "go" | "swift" | "c" | "h" | "cpp" | "java"
             | "kt" | "rb" | "php" | "css" | "html",
@@ -26,16 +85,32 @@ pub(crate) fn file_icon(name: &str) -> IconName {
 
 #[cfg(test)]
 mod tests {
-    use super::{IconName, file_icon};
+    use super::{IconName, IconTheme};
 
     #[test]
     fn a_name_picks_its_icon_by_its_last_extension() {
-        assert_eq!(file_icon("main.RS"), IconName::FileCode);
-        assert_eq!(file_icon("lift.PNG"), IconName::FileImage);
-        assert_eq!(file_icon("notes.md"), IconName::FileText);
-        assert_eq!(file_icon("backup.tar.gz"), IconName::FileArchive);
-        assert_eq!(file_icon(".env"), IconName::FileCog);
-        assert_eq!(file_icon("take.mov"), IconName::FileVideoCamera);
-        assert_eq!(file_icon("Makefile"), IconName::File);
+        assert_eq!(IconTheme::default().file("main.RS"), IconName::FileCode);
+        assert_eq!(IconTheme::default().file("lift.PNG"), IconName::FileImage);
+        assert_eq!(IconTheme::default().file("notes.md"), IconName::FileText);
+        assert_eq!(
+            IconTheme::default().file("backup.tar.gz"),
+            IconName::FileArchive
+        );
+        assert_eq!(IconTheme::default().file(".env"), IconName::FileCog);
+        assert_eq!(
+            IconTheme::default().file("take.mov"),
+            IconName::FileVideoCamera
+        );
+        assert_eq!(IconTheme::default().file("Makefile"), IconName::File);
+    }
+
+    #[test]
+    fn an_owners_rules_come_before_elys_map() {
+        let theme = IconTheme::default()
+            .name("Cargo.toml", IconName::Package)
+            .extension("RS", IconName::Braces);
+        assert_eq!(theme.file("cargo.TOML"), IconName::Package);
+        assert_eq!(theme.file("main.rs"), IconName::Braces);
+        assert_eq!(theme.file("deploy.toml"), IconName::FileCog);
     }
 }
diff --git a/src/primitives/mod.rs b/src/primitives/mod.rs
index 22192ca..efba801 100644
--- a/src/primitives/mod.rs
+++ b/src/primitives/mod.rs
@@ -18,7 +18,8 @@ mod tests;
 pub use backdrop::{Backdrop, Place};
 pub use disclosure::Disclosure;
 pub use divider::Divider;
-pub(crate) use files::file_icon;
+pub use files::IconTheme;
+pub(crate) use files::{file_icon, icon_theme};
 pub use focus::{FocusNext, FocusPrev, FocusRing, FocusScope};
 pub(crate) use focus::{Takeover, give_back, hand_back, hold_focus, tab_stop, take_focus};
 pub use ghost::DragGhost;
diff --git a/src/shell/chrome.rs b/src/shell/chrome.rs
index 6f2e22f..9bfcd78 100644
--- a/src/shell/chrome.rs
+++ b/src/shell/chrome.rs
@@ -9,30 +9,9 @@ use smallvec::SmallVec;
 
 use crate::{
     primitives::{Icon, IconName},
-    theme::{ActiveTheme, ControlSize, IconSize, TextSize},
+    theme::{ActiveTheme, ControlSize, IconSize, Platform, TextSize},
 };
 
-/// Which system's window buttons to draw.
-#[derive(Clone, Copy, Debug, PartialEq, Eq)]
-pub enum ControlsStyle {
-    Mac,
-    Windows,
-    Linux,
-}
-
-impl ControlsStyle {
-    /// The style of the system this build targets.
-    pub fn current() -> Self {
-        if cfg!(target_os = "macos") {
-            Self::Mac
-        } else if cfg!(target_os = "windows") {
-            Self::Windows
-        } else {
-            Self::Linux
-        }
-    }
-}
-
 /// Drags the window, and zooms it on double-click.
 pub fn drag_region(id: impl Into<ElementId>, window: &mut Window, cx: &mut App) -> Stateful<Div> {
     let id = id.into();
@@ -91,7 +70,7 @@ fn run(control: Control, on_close: Option<&OnClose>, window: &mut Window, cx: &m
 #[derive(IntoElement)]
 pub struct WindowControls {
     id: ElementId,
-    style: ControlsStyle,
+    platform: Option<Platform>,
     on_close: Option<OnClose>,
 }
 
@@ -99,13 +78,14 @@ impl WindowControls {
     pub fn new(id: impl Into<ElementId>) -> Self {
         Self {
             id: id.into(),
-            style: ControlsStyle::current(),
+            platform: None,
             on_close: None,
         }
     }
 
-    pub fn style(mut self, style: ControlsStyle) -> Self {
-        self.style = style;
+    /// Draws this platform's buttons instead of the theme's.
+    pub fn platform(mut self, platform: Platform) -> Self {
+        self.platform = Some(platform);
         self
     }
 
@@ -118,10 +98,10 @@ impl WindowControls {
 
 impl RenderOnce for WindowControls {
     fn render(self, window: &mut Window, cx: &mut App) -> impl IntoElement {
-        match self.style {
-            ControlsStyle::Mac => traffic_lights(self.id, self.on_close, window, cx),
-            ControlsStyle::Windows => caption_buttons(self.id, self.on_close, window, cx),
-            ControlsStyle::Linux => round_buttons(self.id, self.on_close, window, cx),
+        match self.platform.unwrap_or(cx.theme().platform) {
+            Platform::Mac => traffic_lights(self.id, self.on_close, window, cx),
+            Platform::Windows => caption_buttons(self.id, self.on_close, window, cx),
+            Platform::Linux => round_buttons(self.id, self.on_close, window, cx),
         }
     }
 }
@@ -304,7 +284,7 @@ fn route_close(id: &ElementId, handler: Option<OnClose>, window: &mut Window, cx
 pub struct TitleBar {
     id: ElementId,
     title: Option<SharedString>,
-    style: Option<ControlsStyle>,
+    platform: Option<Platform>,
     on_close: Option<OnClose>,
     leading: SmallVec<[AnyElement; 2]>,
     actions: SmallVec<[AnyElement; 2]>,
@@ -316,7 +296,7 @@ impl TitleBar {
         Self {
             id: id.into(),
             title: None,
-            style: None,
+            platform: None,
             on_close: None,
             leading: SmallVec::new(),
             actions: SmallVec::new(),
@@ -328,13 +308,13 @@ impl TitleBar {
         self
     }
 
-    /// Draws this style's controls instead of the system's.
-    pub fn style(mut self, style: ControlsStyle) -> Self {
-        self.style = Some(style);
+    /// Draws this platform's controls instead of the system's.
+    pub fn platform(mut self, platform: Platform) -> Self {
+        self.platform = Some(platform);
         self
     }
 
-    /// Runs instead of closing; without a forced style, system closes run it too.
+    /// Runs instead of closing; without a forced platform, system closes run it too.
     pub fn on_close(mut self, handler: impl Fn(&mut Window, &mut App) + 'static) -> Self {
         self.on_close = Some(Rc::new(handler));
         self
@@ -355,19 +335,22 @@ impl ParentElement for TitleBar {
 
 impl RenderOnce for TitleBar {
     fn render(self, window: &mut Window, cx: &mut App) -> impl IntoElement {
-        if self.style.is_none() {
+        if self.platform.is_none() {
             route_close(&self.id, self.on_close.clone(), window, cx);
         }
         let bar = drag_region(self.id, window, cx);
         let theme = cx.theme();
-        let system = self.style.is_none() && cfg!(target_os = "macos");
-        let style = self.style.unwrap_or_else(ControlsStyle::current);
+        let system = self.platform.is_none() && cfg!(target_os = "macos");
+        let style = match system {
+            true => Platform::Mac,
+            false => self.platform.unwrap_or(theme.platform),
+        };
         let mut trailing = (!system).then_some(WindowControls {
             id: "window-controls".into(),
-            style,
+            platform: Some(style),
             on_close: self.on_close,
         });
-        let leading = if style == ControlsStyle::Mac {
+        let leading = if style == Platform::Mac {
             trailing.take()
         } else {
             None
@@ -379,7 +362,7 @@ impl RenderOnce for TitleBar {
                 .text_color(theme.colors.fg_muted)
                 .child(title)
         });
-        let centered = style != ControlsStyle::Windows;
+        let centered = style != Platform::Windows;
         let inset = theme.traffic_light_inset();
         let fullscreen = window.is_fullscreen();
         let bar = bar
@@ -396,9 +379,9 @@ impl RenderOnce for TitleBar {
         let bar = match (system, style) {
             (true, _) if fullscreen => bar.pl_3().pr_2(),
             (true, _) => bar.pl(inset).pr_2(),
-            (false, ControlsStyle::Mac) => bar.pl_3().pr_2().children(leading),
-            (false, ControlsStyle::Windows) => bar.pl_3(),
-            (false, ControlsStyle::Linux) => bar.pl_3().pr_2(),
+            (false, Platform::Mac) => bar.pl_3().pr_2().children(leading),
+            (false, Platform::Windows) => bar.pl_3(),
+            (false, Platform::Linux) => bar.pl_3().pr_2(),
         };
         let bar = bar.children(self.leading);
         let bar = match (centered, title) {
diff --git a/src/shell/mod.rs b/src/shell/mod.rs
index 3d61167..3c30209 100644
--- a/src/shell/mod.rs
+++ b/src/shell/mod.rs
@@ -11,11 +11,12 @@ mod tabs;
 #[cfg(all(test, feature = "test-support"))]
 mod tests;
 mod update;
+mod vibrancy;
 mod windows;
 
 pub use activity::{ActivityBar, ActivityItem};
 pub use bars::{StatusBar, StatusBarItem, Toolbar, ToolbarGroup, ToolbarSeparator};
-pub use chrome::{ControlsStyle, TitleBar, WindowControls, drag_region};
+pub use chrome::{TitleBar, WindowControls, drag_region};
 pub use crash::CrashReporter;
 pub use dialogs::{AboutDialog, SplashScreen};
 pub use frame::ResizeBorder;
@@ -25,4 +26,5 @@ pub use status::{Connectivity, OfflineIndicator, ZoomControl};
 pub use switcher::WindowSwitcher;
 pub use tabs::{TabBar, WindowTab};
 pub use update::{UpdateBanner, UpdateDialog, UpdateState};
+pub use vibrancy::Vibrancy;
 pub use windows::{Corner, Hosted, MiniWindow, WindowManager, open_hosted};
diff --git a/src/shell/tests.rs b/src/shell/tests.rs
index 215d0d2..efe02c5 100644
--- a/src/shell/tests.rs
+++ b/src/shell/tests.rs
@@ -88,3 +88,45 @@ fn the_switcher_switches_on_release_so_its_opener_stays_shut(cx: &mut TestAppCon
     assert!(!desk.read_with(cx, |desk, _| desk.open));
     assert_eq!(desk.read_with(cx, |desk, _| desk.enters_above), above);
 }
+
+struct Platformed;
+
+impl Render for Platformed {
+    fn render(&mut self, _: &mut Window, _: &mut Context<Self>) -> impl IntoElement {
+        div()
+            .flex()
+            .child(
+                div()
+                    .debug_selector(|| "controls".into())
+                    .child(super::WindowControls::new("controls")),
+            )
+            .child(
+                div()
+                    .debug_selector(|| "caps".into())
+                    .child(crate::typography::Kbd::new("secondary-s")),
+            )
+    }
+}
+
+/// Window buttons and key caps follow the theme's platform: Windows draws three wide caption buttons and spells Ctrl.
+#[gpui::test]
+fn the_themes_platform_draws_the_buttons_and_the_caps(cx: &mut TestAppContext) {
+    cx.update(Theme::init);
+    cx.update(|cx| Theme::update(cx, |theme| theme.platform = crate::theme::Platform::Mac));
+    let (_, cx) = cx.add_window_view(|_, _| Platformed);
+    settle(cx);
+    let width = |name: &'static str, cx: &mut VisualTestContext| {
+        cx.debug_bounds(name).expect("a measured part").size.width
+    };
+    let (lights, command) = (width("controls", cx), width("caps", cx));
+    cx.update(|_, cx| Theme::update(cx, |theme| theme.platform = crate::theme::Platform::Windows));
+    settle(cx);
+    assert!(
+        width("controls", cx) > lights * 2.0,
+        "caption buttons wider than lights"
+    );
+    assert!(
+        width("caps", cx) > command,
+        "Ctrl wider than the command mark"
+    );
+}
diff --git a/src/shell/vibrancy.rs b/src/shell/vibrancy.rs
new file mode 100644
index 0000000..e98c9f4
--- /dev/null
+++ b/src/shell/vibrancy.rs
@@ -0,0 +1,42 @@
+use gpui::{
+    AnyElement, App, Div, IntoElement, ParentElement, RenderOnce, StyleRefinement, Styled, Window,
+    div,
+};
+
+use crate::theme::ActiveTheme;
+
+/// A pane the window's blur shows through: vibrancy on macOS, acrylic on Windows. Its window opens with `WindowBackgroundAppearance::Blurred` and nothing opaque beneath the pane; high contrast fills it solid.
+#[derive(IntoElement)]
+pub struct Vibrancy {
+    base: Div,
+}
+
+impl Vibrancy {
+    pub fn new() -> Self {
+        Self { base: div() }
+    }
+}
+
+impl Default for Vibrancy {
+    fn default() -> Self {
+        Self::new()
+    }
+}
+
+impl Styled for Vibrancy {
+    fn style(&mut self) -> &mut StyleRefinement {
+        self.base.style()
+    }
+}
+
+impl ParentElement for Vibrancy {
+    fn extend(&mut self, elements: impl IntoIterator<Item = AnyElement>) {
+        self.base.extend(elements);
+    }
+}
+
+impl RenderOnce for Vibrancy {
+    fn render(self, _: &mut Window, cx: &mut App) -> impl IntoElement {
+        self.base.bg(cx.theme().colors.glass)
+    }
+}
diff --git a/src/theme/mod.rs b/src/theme/mod.rs
index f708322..77fb61b 100644
--- a/src/theme/mod.rs
+++ b/src/theme/mod.rs
@@ -9,6 +9,7 @@ mod media;
 mod messaging;
 mod onboarding;
 mod palette;
+mod platform;
 mod project;
 mod syntax;
 mod tokens;
@@ -32,6 +33,7 @@ pub use media::MediaSizes;
 pub use messaging::MessagingSizes;
 pub use onboarding::OnboardingSizes;
 pub use palette::{HUE_NAMES, Mix, Palette, Syntax};
+pub use platform::Platform;
 pub use project::ProjectSizes;
 pub use syntax::{SyntaxTheme, syntax_themes};
 pub use tokens::{
@@ -69,6 +71,7 @@ pub struct Theme {
     pub font_family: SharedString,
     pub mono_family: SharedString,
     pub reduced_motion: bool,
+    pub platform: Platform,
 }
 
 impl Global for Theme {}
@@ -97,6 +100,7 @@ impl Theme {
             font_family: "Inter".into(),
             mono_family: "JetBrains Mono".into(),
             reduced_motion: false,
+            platform: Platform::current(),
         });
     }
 
diff --git a/src/theme/palette.rs b/src/theme/palette.rs
index 226dafd..9759409 100644
--- a/src/theme/palette.rs
+++ b/src/theme/palette.rs
@@ -116,6 +116,7 @@ mixable!(
         backdrop,
         media_backdrop,
         shimmer,
+        glass,
         shadow,
         tooltip_bg,
         tooltip_fg,
@@ -182,6 +183,7 @@ impl Palette {
             backdrop: rgba(0x18161352).into(),
             media_backdrop: rgba(0x0e0d0bf8).into(),
             shimmer: rgba(0xffffffb3).into(),
+            glass: rgba(0xfcfaf7b8).into(),
             shadow: c(0x181613),
             tooltip_bg: c(0x181613),
             tooltip_fg: c(0xfcfaf7),
@@ -215,6 +217,7 @@ impl Palette {
             palette.fg_subtle = c(0x575552);
             palette.border = c(0xa6a4a2);
             palette.border_strong = c(0x82807d);
+            palette.glass = palette.bg;
         }
         palette
     }
@@ -251,6 +254,7 @@ impl Palette {
             backdrop: rgba(0x00000080).into(),
             media_backdrop: rgba(0x000000f8).into(),
             shimmer: rgba(0xffffff10).into(),
+            glass: rgba(0x131110b8).into(),
             shadow: c(0x000000),
             tooltip_bg: c(0x373533),
             tooltip_fg: c(0xf3f1f0),
@@ -284,6 +288,7 @@ impl Palette {
             palette.fg_subtle = c(0xafadab);
             palette.border = c(0x6a6966);
             palette.border_strong = c(0x858380);
+            palette.glass = palette.bg;
         }
         palette
     }
diff --git a/src/theme/platform.rs b/src/theme/platform.rs
new file mode 100644
index 0000000..be1f1f3
--- /dev/null
+++ b/src/theme/platform.rs
@@ -0,0 +1,20 @@
+/// Whose conventions the components follow: window buttons, the title bar's layout and key caps.
+#[derive(Clone, Copy, Debug, PartialEq, Eq)]
+pub enum Platform {
+    Mac,
+    Windows,
+    Linux,
+}
+
+impl Platform {
+    /// The system this build targets, where the theme starts.
+    pub fn current() -> Self {
+        if cfg!(target_os = "macos") {
+            Platform::Mac
+        } else if cfg!(target_os = "windows") {
+            Platform::Windows
+        } else {
+            Platform::Linux
+        }
+    }
+}
diff --git a/src/theme/tests.rs b/src/theme/tests.rs
index a60b05b..f2b1d73 100644
--- a/src/theme/tests.rs
+++ b/src/theme/tests.rs
@@ -26,7 +26,7 @@ fn every_color_answers_to_its_name() {
     for (ix, name) in Palette::NAMES.iter().enumerate() {
         *palette.token_mut(name) = hsla(ix as f32 / 64.0, 0.5, 0.5, 1.0);
     }
-    assert_eq!(Palette::NAMES.len(), 35, "every color of the palette");
+    assert_eq!(Palette::NAMES.len(), 36, "every color of the palette");
     let at = |name: &str| {
         Palette::NAMES
             .iter()
@@ -50,3 +50,18 @@ fn every_color_answers_to_its_name() {
 fn an_unknown_color_fails() {
     Palette::light(false).token_mut("glow");
 }
+
+#[test]
+fn glass_lets_the_blur_through_until_high_contrast() {
+    for (plain, strong) in [
+        (Palette::light(false), Palette::light(true)),
+        (Palette::dark(false), Palette::dark(true)),
+    ] {
+        assert!(
+            plain.glass.a > 0.0 && plain.glass.a < 1.0,
+            "{:?}",
+            plain.glass
+        );
+        assert_eq!(strong.glass, strong.bg);
+    }
+}
diff --git a/src/typography/inline.rs b/src/typography/inline.rs
index 4a7e331..76ddfb0 100644
--- a/src/typography/inline.rs
+++ b/src/typography/inline.rs
@@ -7,8 +7,8 @@ use gpui::{
 use regex::RegexBuilder;
 use smallvec::SmallVec;
 
-use super::keys::{Platform, keystroke_labels};
-use crate::theme::{ActiveTheme, Radius, TextSize};
+use super::keys::{keystroke, keystroke_labels};
+use crate::theme::{ActiveTheme, Platform, Radius, TextSize};
 
 /// Monospace fragment on a quiet fill.
 #[derive(IntoElement)]
@@ -56,28 +56,25 @@ fn cap(label: String, cx: &App) -> impl IntoElement + use<> {
         .child(label)
 }
 
-fn parse(source: &str) -> Keystroke {
-    Keystroke::parse(source).unwrap_or_else(|error| panic!("bad keystroke {source:?}: {error}"))
-}
-
-/// One key, labeled for this platform. Takes gpui key syntax.
+/// One key, labeled for the theme's platform. Takes gpui key syntax.
 #[derive(IntoElement)]
 pub struct Kbd {
-    stroke: Keystroke,
+    source: SharedString,
 }
 
 impl Kbd {
-    /// `"secondary-s"` reads ⌘S on macOS and Ctrl S elsewhere.
+    /// `"secondary-s"` reads ⌘S for the Mac and Ctrl S for the others.
     pub fn new(source: &str) -> Self {
         Self {
-            stroke: parse(source),
+            source: SharedString::from(source.to_string()),
         }
     }
 }
 
 impl RenderOnce for Kbd {
     fn render(self, _: &mut Window, cx: &mut App) -> impl IntoElement {
-        let labels = keystroke_labels(&self.stroke, Platform::current());
+        let platform = cx.theme().platform;
+        let labels = keystroke_labels(&keystroke(&self.source, platform), platform);
         div()
             .flex()
             .gap_0p5()
@@ -88,27 +85,32 @@ impl RenderOnce for Kbd {
 /// A chord sequence such as `"cmd-k cmd-s"`.
 #[derive(IntoElement)]
 pub struct KbdCombo {
-    strokes: SmallVec<[Keystroke; 2]>,
+    source: SharedString,
 }
 
 impl KbdCombo {
     pub fn new(source: &str) -> Self {
         Self {
-            strokes: source.split_whitespace().map(parse).collect(),
+            source: SharedString::from(source.to_string()),
         }
     }
 }
 
 impl RenderOnce for KbdCombo {
     fn render(self, _: &mut Window, cx: &mut App) -> impl IntoElement {
-        let platform = Platform::current();
+        let platform = cx.theme().platform;
+        let strokes: Vec<Keystroke> = self
+            .source
+            .split_whitespace()
+            .map(|source| keystroke(source, platform))
+            .collect();
         let subtle = cx.theme().colors.fg_subtle;
         let spelled = platform != Platform::Mac;
         div()
             .flex()
             .items_center()
             .gap_2()
-            .children(self.strokes.iter().map(|stroke| {
+            .children(strokes.iter().map(|stroke| {
                 let labels = keystroke_labels(stroke, platform);
                 let last = labels.len() - 1;
                 div().flex().items_center().gap_0p5().children(
diff --git a/src/typography/keys.rs b/src/typography/keys.rs
index c6b7851..3107c6e 100644
--- a/src/typography/keys.rs
+++ b/src/typography/keys.rs
@@ -1,22 +1,20 @@
 use gpui::Keystroke;
 
-#[derive(Clone, Copy, Debug, PartialEq, Eq)]
-pub enum Platform {
-    Mac,
-    Windows,
-    Linux,
-}
+use crate::theme::Platform;
 
-impl Platform {
-    pub fn current() -> Self {
-        if cfg!(target_os = "macos") {
-            Platform::Mac
-        } else if cfg!(target_os = "windows") {
-            Platform::Windows
-        } else {
-            Platform::Linux
-        }
-    }
+/// One keystroke in gpui key syntax, `secondary` read for `platform`: Command on the Mac, Control elsewhere.
+pub fn keystroke(source: &str, platform: Platform) -> Keystroke {
+    let secondary = if platform == Platform::Mac {
+        "cmd"
+    } else {
+        "ctrl"
+    };
+    let spelled: Vec<&str> = source
+        .split('-')
+        .map(|part| if part == "secondary" { secondary } else { part })
+        .collect();
+    Keystroke::parse(&spelled.join("-"))
+        .unwrap_or_else(|error| panic!("bad keystroke {source:?}: {error}"))
 }
 
 /// Caps for one keystroke, modifiers first, in platform order.
@@ -94,6 +92,17 @@ mod tests {
         assert_eq!(labels, ["Super", "Esc"]);
     }
 
+    #[test]
+    fn secondary_reads_for_the_platform() {
+        let mac = keystroke_labels(&keystroke("secondary-s", Platform::Mac), Platform::Mac);
+        assert_eq!(mac, ["⌘", "S"]);
+        let windows = Platform::Windows;
+        assert_eq!(
+            keystroke_labels(&keystroke("secondary-s", windows), windows),
+            ["Ctrl", "S"]
+        );
+    }
+
     #[test]
     fn keys_keep_their_names_or_upper_case() {
         assert_eq!(key_label("f12", Platform::Mac), "F12");
diff --git a/tasks/ch31-43.md b/tasks/ch31-43.md
index 3fc4b24..7b17531 100644
--- a/tasks/ch31-43.md
+++ b/tasks/ch31-43.md
@@ -266,9 +266,10 @@
 
 ## T39c Theme · Platform
 
-- [ ] IconThemeProvider
-- [ ] Platform Style
-- [ ] VibrancyBackground / Mica / Acrylic — native `WindowBackgroundAppearance::Blurred`
+- [x] IconThemeProvider → `primitives::IconTheme`, an owner's rules by name and extension over `file_icon`
+- [x] Platform Style → `theme::Platform`, the theme's `platform`: the window buttons Ely draws, the title bar, key caps
+- [x] VibrancyBackground / Acrylic → `shell::Vibrancy` in a window opened `WindowBackgroundAppearance::Blurred`
+- [ ] Mica — blocked: gpui 0.2.2's one blur, `Blurred`, is acrylic on Windows
 
 ## T40 i18n & a11y — `src/i18n`