diff --git a/AGENTS.md b/AGENTS.md
index 1855b6f..b6c82b7 100644
--- a/AGENTS.md
+++ b/AGENTS.md
@@ -153,7 +153,7 @@ Ely GPUI Component. A component library for GPUI, in light and dark.
 - A row that holds text beside fixed parts lets the text give way: the text takes `flex_1().min_w_0()` and an `Ellipsis`; counts, icons, dates and chevrons take `flex_none`. A label that must stay whole wraps in that block instead, as `forms::Checkbox`'s does.
 - A mark over a text field reads the field at paint time, from a canvas laid over it (`collab::RemoteCursor`): by then `TextInput::bounds_for` holds this frame's layout, and a still page never renders again to catch up.
 - A callback field holds a named `type` alias; clippy's type_complexity rejects `Option<Rc<dyn Fn(..)>>`. A chapter shares one alias per shape.
-- A component that fills its container takes no width on its root: a block or a flex column stretches it. Percents fill badly in taffy 0.9. `w_full` in a flex column that a block measures by content keeps its content's width: taffy lays the column out once at unknown width and keeps that layout when the width comes out the same. `min_w_full` resolves against a block's outer width, padding and all (`forms::FormField`). In a flex row the host gives it `flex_1`; as a window's root it sits in a `size_full` box. A root centered under a cap keeps `w_full`, since `mx_auto` needs a width to fill (`layout::Container`); so does one that keeps a ratio, since taffy 0.9 follows a ratio from a set width, not a stretch (`layout::AspectRatio`). A row that hands a text field a `flex_1` share keeps `w_full` too: stretched without a width, taffy 0.9 can keep a pass that laid the share at no width, and the field draws nothing (`forms::Input`, `InputGroup`, `TagInput`).
+- A component that fills its container takes no width on its root: a block or a flex column stretches it. Percents fill badly in taffy 0.9. `w_full` in a flex column that a block measures by content keeps its content's width: taffy lays the column out once at unknown width and keeps that layout when the width comes out the same. `min_w_full` resolves against a block's outer width, padding and all (`forms::FormField`). In a flex row the host gives it `flex_1`; as a window's root it sits in a `size_full` box. A root centered under a cap keeps `w_full`, since `mx_auto` needs a width to fill (`layout::Container`); so does one that keeps a ratio, since taffy 0.9 follows a ratio from a set width, not a stretch (`layout::AspectRatio`, and `primitives::framed` under VideoPlayer, CameraPreview, ModelViewer, ParticipantTile and InpaintCanvas). A row that hands the text field element itself a `flex_1` share keeps `w_full` too: stretched without a width, taffy 0.9 can keep a pass that laid the share at no width, and the field draws nothing (`forms::Input`, `InputGroup`, `TagInput`); a row around one of those, as `NumberInput`'s is, takes none. `Button::full_width` is its host asking, since a button takes no style. Each chapter's test holds its filling roots at the full width of such a column through `layout::tests::narrow_width`, which reads a root by its `debug_selector`.
 - A field's `Highlight` sets color, wash, weight, slant and strike per span; measuring and painting share one set of runs, so wrapped heights match.
 - A block editor keeps one undo for the document: text and structure together, as snapshots through `forms::History`; it takes Undo and Redo before its fields do.
 - gpui calls focus listeners only while the window is active. A test that needs focus events activates its window with `window.activate_window()`.
diff --git a/TASKS.md b/TASKS.md
index 9ec4b8f..4957d2a 100644
--- a/TASKS.md
+++ b/TASKS.md
@@ -473,3 +473,4 @@ Per-component lines live in `tasks/`. Tags there:
 | T43c | 1 | FAIL | the audit left fg_subtle on active and every syntax color unread, both under 4.5:1; the viewer left out avatar and container sizes while claiming every token |
 | T43c | 2 | PASS | the AGENTS.md decision narrowed to the pairs the audit holds, in the pass commit |
 | T44a | 1 | FAIL | twelve roots in nine components still said w_full: a root held in a variable, a match arm or an animation passed the sweep |
+| T44a | 2 | FAIL | roots built in render(mut self), returned by shared helpers or passed through them still said w_full: fields, charts, state views, Steps, previews; five measured at content width in a padded card |
diff --git a/examples/gallery/pages/feedback/messages.rs b/examples/gallery/pages/feedback/messages.rs
index 31bf43a..fdc4bdb 100644
--- a/examples/gallery/pages/feedback/messages.rs
+++ b/examples/gallery/pages/feedback/messages.rs
@@ -358,7 +358,7 @@ pub fn empties(cx: &mut App) -> impl IntoElement + use<> {
             .min_w_0()
             .h_80()
             .flex()
-            .items_center()
+            .flex_col()
             .justify_center()
             .rounded(theme.radius(Radius::Lg))
             .border_1()
diff --git a/examples/gallery/pages/feedback/states.rs b/examples/gallery/pages/feedback/states.rs
index c494e58..cc2c4fb 100644
--- a/examples/gallery/pages/feedback/states.rs
+++ b/examples/gallery/pages/feedback/states.rs
@@ -26,7 +26,7 @@ fn frame(cx: &App) -> Div {
         .min_w_0()
         .h_80()
         .flex()
-        .items_center()
+        .flex_col()
         .justify_center()
         .rounded(theme.radius(Radius::Lg))
         .border_1()
diff --git a/src/agent/previews.rs b/src/agent/previews.rs
index 0e2c713..c100de3 100644
--- a/src/agent/previews.rs
+++ b/src/agent/previews.rs
@@ -56,7 +56,7 @@ fn address_bar(
 fn card(cx: &App) -> Div {
     let theme = cx.theme();
     div()
-        .w_full()
+        .debug_selector(|| "preview-root".into())
         .flex()
         .flex_col()
         .rounded(theme.radius(Radius::Lg))
@@ -395,7 +395,7 @@ impl RenderOnce for LivePreview {
                 .into_any_element()
         });
         card(cx)
-            .size_full()
+            .h_full()
             .child(address_bar(&self.id, self.url, self.updating, reload, cx))
             .child(
                 div()
diff --git a/src/agent/tests/previews.rs b/src/agent/tests/previews.rs
index aa22321..50b823d 100644
--- a/src/agent/tests/previews.rs
+++ b/src/agent/tests/previews.rs
@@ -7,8 +7,9 @@ use gpui::{
 
 use super::{press, settle};
 use crate::{
-    agent::{ArtifactPanel, BrowserPreview, ComputerUseViewer},
+    agent::{ArtifactPanel, BrowserPreview, ComputerUseViewer, LivePreview},
     forms,
+    layout::tests::narrow_width,
     primitives::{FocusNext, IconName},
     theme::{ActiveTheme, AvatarSize, Theme},
 };
@@ -288,3 +289,24 @@ fn a_screen_takes_its_pictures_shape(cx: &mut TestAppContext) {
         height.get()
     );
 }
+
+#[gpui::test]
+fn previews_fill_a_column_their_block_measures_by_content(cx: &mut TestAppContext) {
+    setup(cx);
+    let widths = [
+        narrow_width(cx, "preview-root", |_, _| {
+            BrowserPreview::new("browser", "localhost", ["a.png"], 0).into_any_element()
+        }),
+        narrow_width(cx, "preview-root", |_, _| {
+            ComputerUseViewer::new("screen", "a.png").into_any_element()
+        }),
+        narrow_width(cx, "preview-root", |_, _| {
+            LivePreview::new("live", "localhost", div()).into_any_element()
+        }),
+    ];
+    assert_eq!(
+        widths,
+        [px(240.0); 3],
+        "each preview spans the card inside its padding"
+    );
+}
diff --git a/src/charts/calendar.rs b/src/charts/calendar.rs
index 039549e..1b8dd16 100644
--- a/src/charts/calendar.rs
+++ b/src/charts/calendar.rs
@@ -1,8 +1,8 @@
 use std::rc::Rc;
 
 use gpui::{
-    App, Div, ElementId, Entity, Hsla, IntoElement, ParentElement, Pixels, Refineable, RenderOnce,
-    StyleRefinement, Styled, Window, canvas, div, fill,
+    App, Div, ElementId, Entity, Hsla, InteractiveElement, IntoElement, ParentElement, Pixels,
+    Refineable, RenderOnce, StyleRefinement, Styled, Window, canvas, div, fill,
 };
 use jiff::{Span, civil::Date};
 
@@ -157,7 +157,9 @@ impl RenderOnce for CalendarHeatmap {
         );
         let hit = days.iter().map(|(rect, _)| *rect).collect::<Vec<_>>();
         let legend = key(shades, ("Less", "More"), cx);
-        let mut root = div().w_full().h(sizes.height * 0.5);
+        let mut root = div()
+            .debug_selector(|| "chart-root".into())
+            .h(sizes.height * 0.5);
         root.style().refine(self.base.style());
         let chart = tracked(
             div().relative().flex_1().min_h_0(),
diff --git a/src/charts/cartesian.rs b/src/charts/cartesian.rs
index c536f39..ae961e0 100644
--- a/src/charts/cartesian.rs
+++ b/src/charts/cartesian.rs
@@ -1,8 +1,8 @@
 use std::{collections::HashSet, rc::Rc};
 
 use gpui::{
-    App, Div, ElementId, IntoElement, Refineable, RenderOnce, SharedString, StyleRefinement,
-    Styled, Window, div,
+    App, Div, ElementId, InteractiveElement, IntoElement, Refineable, RenderOnce, SharedString,
+    StyleRefinement, Styled, Window, div,
 };
 
 use super::{
@@ -131,7 +131,9 @@ impl Chart {
 
 /// Renders a plot at the theme's chart height unless the owner sizes it.
 pub(crate) fn sized(base: &mut Div, plotted: Plot, window: &mut Window, cx: &mut App) -> Div {
-    let mut frame = div().w_full().h(cx.theme().chart().height);
+    let mut frame = div()
+        .debug_selector(|| "chart-root".into())
+        .h(cx.theme().chart().height);
     frame.style().refine(base.style());
     plot(plotted, frame, window, cx)
 }
diff --git a/src/charts/flow.rs b/src/charts/flow.rs
index 8793b93..818e14c 100644
--- a/src/charts/flow.rs
+++ b/src/charts/flow.rs
@@ -342,7 +342,10 @@ impl RenderOnce for SankeyChart {
         let palette = colors.clone();
         let (hit_nodes, hit_ribbons) = (nodes, ribbons);
         let (moved, left) = (flows.clone(), flows.clone());
-        let mut root = div().relative().w_full().h(sizes.height);
+        let mut root = div()
+            .debug_selector(|| "chart-root".into())
+            .relative()
+            .h(sizes.height);
         root.style().refine(self.base.style());
         root.id((self.id.clone(), "sankey"))
             .on_mouse_move(move |event: &MouseMoveEvent, _, cx| {
diff --git a/src/charts/funnel.rs b/src/charts/funnel.rs
index 4b7afb1..f8ac018 100644
--- a/src/charts/funnel.rs
+++ b/src/charts/funnel.rs
@@ -184,7 +184,10 @@ impl RenderOnce for FunnelChart {
             frame.h / self.stages.len().max(1) as f32,
         );
         let count = self.stages.len();
-        let mut root = div().relative().w_full().h(sizes.height);
+        let mut root = div()
+            .debug_selector(|| "chart-root".into())
+            .relative()
+            .h(sizes.height);
         root.style().refine(self.base.style());
         root.id((self.id.clone(), "funnel"))
             .on_mouse_move(move |event: &MouseMoveEvent, _, cx| {
diff --git a/src/charts/network.rs b/src/charts/network.rs
index bb426ab..c51e6cf 100644
--- a/src/charts/network.rs
+++ b/src/charts/network.rs
@@ -287,7 +287,10 @@ impl RenderOnce for NetworkGraph {
             graph.clone(),
         );
         let press_hit = hit.clone();
-        let mut root = div().relative().w_full().h(sizes.height);
+        let mut root = div()
+            .debug_selector(|| "chart-root".into())
+            .relative()
+            .h(sizes.height);
         root.style().refine(self.base.style());
         root.id((self.id.clone(), "network"))
             .on_mouse_down(MouseButton::Left, move |event: &MouseDownEvent, _, cx| {
diff --git a/src/charts/parallel.rs b/src/charts/parallel.rs
index 5d4dacc..de50bd5 100644
--- a/src/charts/parallel.rs
+++ b/src/charts/parallel.rs
@@ -1,8 +1,8 @@
 use std::rc::Rc;
 
 use gpui::{
-    App, Div, ElementId, Entity, IntoElement, ParentElement, PathBuilder, Pixels, Refineable,
-    RenderOnce, SharedString, StyleRefinement, Styled, Window, canvas, div,
+    App, Div, ElementId, Entity, InteractiveElement, IntoElement, ParentElement, PathBuilder,
+    Pixels, Refineable, RenderOnce, SharedString, StyleRefinement, Styled, Window, canvas, div,
 };
 
 use super::{
@@ -215,7 +215,10 @@ impl RenderOnce for ParallelCoordinates {
             lines.clone(),
         );
         let reach = pixels(sizes.inset);
-        let mut root = div().relative().w_full().h(sizes.height);
+        let mut root = div()
+            .debug_selector(|| "chart-root".into())
+            .relative()
+            .h(sizes.height);
         root.style().refine(self.base.style());
         tracked(
             root,
diff --git a/src/charts/pie.rs b/src/charts/pie.rs
index de11c3b..6d16c7b 100644
--- a/src/charts/pie.rs
+++ b/src/charts/pie.rs
@@ -302,7 +302,7 @@ impl RenderOnce for PieChart {
             |legend, (ix, (name, _))| legend.entry(tint(&colors, ix), name.clone(), false),
         );
         let (moved, left, measured, hit) = (ring.clone(), ring.clone(), ring.clone(), arcs.clone());
-        let mut frame = div().w_full().h(sizes.height);
+        let mut frame = div().debug_selector(|| "chart-root".into()).h(sizes.height);
         frame.style().refine(self.base.style());
         frame.flex().flex_col().gap_2().child(legend).child(
             div()
diff --git a/src/charts/radar.rs b/src/charts/radar.rs
index c7b79ea..1be6c12 100644
--- a/src/charts/radar.rs
+++ b/src/charts/radar.rs
@@ -245,7 +245,7 @@ impl RenderOnce for RadarChart {
         let (stroke, hairline) = (sizes.stroke.to_pixels(rem), sizes.hairline);
         let palette = colors.clone();
         let (moved, left, measured) = (radar.clone(), radar.clone(), radar.clone());
-        let mut frame = div().w_full().h(sizes.height);
+        let mut frame = div().debug_selector(|| "chart-root".into()).h(sizes.height);
         frame.style().refine(self.base.style());
         frame.flex().flex_col().gap_2().children(legend).child(
             div()
diff --git a/src/charts/realtime.rs b/src/charts/realtime.rs
index a97d441..c1211fa 100644
--- a/src/charts/realtime.rs
+++ b/src/charts/realtime.rs
@@ -1,8 +1,9 @@
 use std::time::Instant;
 
 use gpui::{
-    App, Bounds, ContentMask, Div, ElementId, Entity, IntoElement, ParentElement, PathBuilder,
-    Pixels, Refineable, RenderOnce, StyleRefinement, Styled, Window, canvas, div, fill, size,
+    App, Bounds, ContentMask, Div, ElementId, Entity, InteractiveElement, IntoElement,
+    ParentElement, PathBuilder, Pixels, Refineable, RenderOnce, StyleRefinement, Styled, Window,
+    canvas, div, fill, size,
 };
 
 use super::{
@@ -128,7 +129,10 @@ impl RenderOnce for RealtimeChart {
             pixels(sizes.inset),
         );
         let measured = live.clone();
-        let mut chart = div().relative().w_full().h(sizes.height * 0.6);
+        let mut chart = div()
+            .debug_selector(|| "chart-root".into())
+            .relative()
+            .h(sizes.height * 0.6);
         chart.style().refine(self.base.style());
         chart
             .child(
diff --git a/src/charts/relations.rs b/src/charts/relations.rs
index ee8cc22..01eb0b9 100644
--- a/src/charts/relations.rs
+++ b/src/charts/relations.rs
@@ -222,7 +222,10 @@ impl RenderOnce for ChordDiagram {
             })
             .collect();
         let (palette, arcs, hit) = (colors.clone(), groups.clone(), groups);
-        let mut root = div().relative().w_full().h(sizes.height);
+        let mut root = div()
+            .debug_selector(|| "chart-root".into())
+            .relative()
+            .h(sizes.height);
         root.style().refine(self.base.style());
         tracked(
             root,
diff --git a/src/charts/schedule.rs b/src/charts/schedule.rs
index 266c5eb..5e6f8d0 100644
--- a/src/charts/schedule.rs
+++ b/src/charts/schedule.rs
@@ -1,6 +1,7 @@
 use gpui::{
-    App, Bounds, Div, ElementId, Entity, IntoElement, ParentElement, PathBuilder, Pixels,
-    Refineable, RenderOnce, SharedString, StyleRefinement, Styled, Window, canvas, div, fill, size,
+    App, Bounds, Div, ElementId, Entity, InteractiveElement, IntoElement, ParentElement,
+    PathBuilder, Pixels, Refineable, RenderOnce, SharedString, StyleRefinement, Styled, Window,
+    canvas, div, fill, size,
 };
 use jiff::{
     Span,
@@ -267,8 +268,8 @@ impl RenderOnce for GanttChart {
         );
         let painted = bars.clone();
         let mut root = div()
+            .debug_selector(|| "chart-root".into())
             .relative()
-            .w_full()
             .h(sizes.foot + theme.table_row(Density::Compact) * count as f32);
         root.style().refine(self.base.style());
         tracked(
diff --git a/src/charts/sunburst.rs b/src/charts/sunburst.rs
index 3f8189d..0e38f27 100644
--- a/src/charts/sunburst.rs
+++ b/src/charts/sunburst.rs
@@ -187,7 +187,10 @@ impl RenderOnce for Sunburst {
             );
         let (moved, left, measured, hit) = (ring.clone(), ring.clone(), ring.clone(), arcs.clone());
         let painted = arcs.clone();
-        let mut frame = div().relative().w_full().h(sizes.height);
+        let mut frame = div()
+            .debug_selector(|| "chart-root".into())
+            .relative()
+            .h(sizes.height);
         frame.style().refine(self.base.style());
         frame
             .id((self.id.clone(), "ring"))
diff --git a/src/charts/targets.rs b/src/charts/targets.rs
index aec26c2..7b94062 100644
--- a/src/charts/targets.rs
+++ b/src/charts/targets.rs
@@ -193,8 +193,8 @@ impl RenderOnce for BulletChart {
             colors.clone(),
         );
         let mut root = div()
+            .debug_selector(|| "chart-root".into())
             .relative()
-            .w_full()
             .h(theme.table_row(Density::Comfortable) * count as f32);
         root.style().refine(self.base.style());
         tracked(
diff --git a/src/charts/tests.rs b/src/charts/tests.rs
index 9ad9a72..6bd47ed 100644
--- a/src/charts/tests.rs
+++ b/src/charts/tests.rs
@@ -10,11 +10,12 @@ use gpui::{
 use jiff::civil::date;
 
 use super::{
-    BarChart, Bullet, BulletChart, CalendarHeatmap, ChartLegend, ChordDiagram, FunnelChart,
-    GanttChart, HeatmapChart, LineChart, NetworkGraph, ParallelCoordinates, ProgressChart,
-    RadarChart, SankeyChart, Series, Task, Treemap,
+    AreaChart, BarChart, BoxPlot, Bullet, BulletChart, CalendarHeatmap, ChartLegend, ChordDiagram,
+    FunnelChart, GanttChart, HeatmapChart, Histogram, LineChart, NetworkGraph, ParallelCoordinates,
+    PieChart, Points, ProgressChart, RadarChart, RealtimeChart, SankeyChart, ScatterChart, Series,
+    Slice, Sunburst, Task, Treemap, ViolinPlot, WaterfallChart,
 };
-use crate::theme::Theme;
+use crate::{layout::tests::narrow_width, theme::Theme};
 
 #[gpui::test]
 fn a_chart_exports_as_svg_and_csv(cx: &mut TestAppContext) {
@@ -208,3 +209,124 @@ fn tab_reaches_a_legend_entry_and_enter_toggles_it(cx: &mut TestAppContext) {
     settle(cx);
     assert_eq!(*heard.borrow(), ["Held out"]);
 }
+
+#[gpui::test]
+fn every_chart_fills_a_column_its_block_measures_by_content(cx: &mut TestAppContext) {
+    cx.update(Theme::init);
+    let two = || Series::new("s", [1.0, 2.0]);
+    let pairs = [vec![0.0, 1.0], vec![1.0, 0.0]];
+    let widths = [
+        narrow_width(cx, "chart-root", move |_, _| {
+            LineChart::new("line", ["a", "b"])
+                .series(two())
+                .into_any_element()
+        }),
+        narrow_width(cx, "chart-root", move |_, _| {
+            AreaChart::new("area", ["a", "b"])
+                .series(two())
+                .into_any_element()
+        }),
+        narrow_width(cx, "chart-root", move |_, _| {
+            BarChart::new("bar", ["a", "b"])
+                .series(two())
+                .into_any_element()
+        }),
+        narrow_width(cx, "chart-root", |_, _| {
+            let points = Points::new("p", [(0.0, 1.0), (1.0, 2.0)]);
+            ScatterChart::new("scatter")
+                .points(points)
+                .into_any_element()
+        }),
+        narrow_width(cx, "chart-root", |_, _| {
+            Histogram::new("histogram", [1.0, 2.0, 2.0, 3.0]).into_any_element()
+        }),
+        narrow_width(cx, "chart-root", |_, _| {
+            WaterfallChart::new("waterfall")
+                .step("a", 2.0)
+                .step("b", -1.0)
+                .into_any_element()
+        }),
+        narrow_width(cx, "chart-root", |_, _| {
+            BoxPlot::new("box")
+                .group("a", [1.0, 2.0, 3.0])
+                .into_any_element()
+        }),
+        narrow_width(cx, "chart-root", |_, _| {
+            ViolinPlot::new("violin")
+                .group("a", [1.0, 2.0, 3.0])
+                .into_any_element()
+        }),
+        narrow_width(cx, "chart-root", |_, _| {
+            CalendarHeatmap::new("days", date(2026, 1, 5), [1.0; 14]).into_any_element()
+        }),
+        narrow_width(cx, "chart-root", |_, _| {
+            SankeyChart::new("sankey", ["a", "b"])
+                .link(0, 1, 5.0)
+                .into_any_element()
+        }),
+        narrow_width(cx, "chart-root", |_, _| {
+            FunnelChart::new("funnel")
+                .stage("a", 2.0)
+                .stage("b", 1.0)
+                .into_any_element()
+        }),
+        narrow_width(cx, "chart-root", |_, _| {
+            NetworkGraph::new("network")
+                .node("a", 0)
+                .node("b", 0)
+                .edge(0, 1)
+                .into_any_element()
+        }),
+        narrow_width(cx, "chart-root", |_, _| {
+            ParallelCoordinates::new("parallel", ["a", "b"])
+                .record("r", [1.0, 2.0])
+                .into_any_element()
+        }),
+        narrow_width(cx, "chart-root", |_, _| {
+            PieChart::new("pie")
+                .slice("a", 1.0)
+                .slice("b", 2.0)
+                .into_any_element()
+        }),
+        narrow_width(cx, "chart-root", move |_, _| {
+            RadarChart::new("radar", ["a", "b", "c"])
+                .series(Series::new("s", [1.0, 2.0, 3.0]))
+                .into_any_element()
+        }),
+        narrow_width(cx, "chart-root", |_, _| {
+            RealtimeChart::new("live", [1.0, 2.0], 2).into_any_element()
+        }),
+        narrow_width(cx, "chart-root", move |_, _| {
+            ChordDiagram::new("chord", ["a", "b"], pairs.to_vec()).into_any_element()
+        }),
+        narrow_width(cx, "chart-root", |_, _| {
+            GanttChart::new("gantt")
+                .task(Task::new("t", date(2026, 3, 1), date(2026, 3, 9)))
+                .into_any_element()
+        }),
+        narrow_width(cx, "chart-root", |_, _| {
+            Sunburst::new("sun", [Slice::new("a", 1.0)]).into_any_element()
+        }),
+        narrow_width(cx, "chart-root", |_, _| {
+            BulletChart::new("bullets")
+                .bullet(Bullet::new("b", 5.0, 8.0))
+                .into_any_element()
+        }),
+        narrow_width(cx, "chart-root", |_, _| {
+            Treemap::new("treemap")
+                .tile("a", 1.0)
+                .tile("b", 2.0)
+                .into_any_element()
+        }),
+        narrow_width(cx, "chart-root", |_, _| {
+            HeatmapChart::new("heatmap", ["a"])
+                .row("a", [1.0])
+                .into_any_element()
+        }),
+    ];
+    assert_eq!(
+        widths,
+        [px(240.0); 22],
+        "each chart spans the card inside its padding"
+    );
+}
diff --git a/src/charts/tiles.rs b/src/charts/tiles.rs
index 4b5e775..16caf1a 100644
--- a/src/charts/tiles.rs
+++ b/src/charts/tiles.rs
@@ -208,7 +208,10 @@ impl RenderOnce for Treemap {
             rects.clone(),
             rects,
         );
-        let mut root = div().relative().w_full().h(sizes.height);
+        let mut root = div()
+            .debug_selector(|| "chart-root".into())
+            .relative()
+            .h(sizes.height);
         root.style().refine(self.base.style());
         tracked(
             root,
@@ -406,7 +409,10 @@ impl RenderOnce for HeatmapChart {
             sizes.hairline,
         );
         let legend = key(steps(ink), ("Less", "More"), cx);
-        let mut root = div().relative().w_full().h(sizes.height);
+        let mut root = div()
+            .debug_selector(|| "chart-root".into())
+            .relative()
+            .h(sizes.height);
         root.style().refine(self.base.style());
         let chart = tracked(
             div().relative().flex_1().min_h_0(),
diff --git a/src/devtools/structure.rs b/src/devtools/structure.rs
index e1697b1..7e14f68 100644
--- a/src/devtools/structure.rs
+++ b/src/devtools/structure.rs
@@ -410,6 +410,17 @@ impl RenderOnce for IndexManager {
         );
         let ready = !name.read(cx).text().trim().is_empty() && !picked.is_empty();
         let [chose, flipped, pick_method, made] = [(); 4].map(|_| draft.clone());
+        let methods = Select::new(
+            (id.clone(), "method"),
+            METHODS.iter().map(|method| Choice::new(*method, *method)),
+        )
+        .selected(method)
+        .on_change(move |value, _, cx| {
+            pick_method.update(cx, |draft, cx| {
+                draft.method = value.clone();
+                cx.notify();
+            })
+        });
         div()
             .flex()
             .flex_col()
@@ -453,19 +464,7 @@ impl RenderOnce for IndexManager {
                                         })
                                     }),
                             )
-                            .child(
-                                Select::new(
-                                    (id.clone(), "method"),
-                                    METHODS.iter().map(|method| Choice::new(*method, *method)),
-                                )
-                                .selected(method)
-                                .on_change(move |value, _, cx| {
-                                    pick_method.update(cx, |draft, cx| {
-                                        draft.method = value.clone();
-                                        cx.notify();
-                                    })
-                                }),
-                            ),
+                            .child(div().flex_1().min_w_0().child(methods)),
                     )
                     .child(
                         Button::new((id, "create"), "Create index")
diff --git a/src/feedback/notification.rs b/src/feedback/notification.rs
index d96b72c..bf558aa 100644
--- a/src/feedback/notification.rs
+++ b/src/feedback/notification.rs
@@ -248,7 +248,7 @@ impl RenderOnce for NotificationCenter {
             div()
                 .flex_1()
                 .flex()
-                .items_center()
+                .flex_col()
                 .justify_center()
                 .child(
                     EmptyState::new(
diff --git a/src/feedback/states.rs b/src/feedback/states.rs
index 7ae69fc..208bc0f 100644
--- a/src/feedback/states.rs
+++ b/src/feedback/states.rs
@@ -53,7 +53,7 @@ pub(super) fn state_view(
     let theme = cx.theme();
     let colors = &theme.colors;
     div()
-        .w_full()
+        .debug_selector(|| "state-root".into())
         .flex()
         .flex_col()
         .items_center()
diff --git a/src/feedback/tests/states.rs b/src/feedback/tests/states.rs
index 7f4a77e..08e720c 100644
--- a/src/feedback/tests/states.rs
+++ b/src/feedback/tests/states.rs
@@ -10,8 +10,10 @@ use super::{press, settle, setup, wait};
 use crate::{
     buttons::Button,
     feedback::{
-        ConfirmationCard, Countdown, EmptyState, ErrorBoundary, SaveState, SavingIndicator,
+        ConfirmationCard, Countdown, EmptyState, ErrorBoundary, ErrorView, ResultView, SaveState,
+        SavingIndicator,
     },
+    layout::tests::narrow_width,
     primitives::{FocusScope, IconName, Measure},
 };
 
@@ -200,3 +202,24 @@ fn a_long_inline_message_wraps_inside_its_box(cx: &mut TestAppContext) {
         .expect("the words draw");
     assert!(text.right() <= px(200.0), "{text:?}");
 }
+
+#[gpui::test]
+fn state_views_fill_a_column_their_block_measures_by_content(cx: &mut TestAppContext) {
+    setup(cx);
+    let widths = [
+        narrow_width(cx, "state-root", |_, _| {
+            EmptyState::new("empty", IconName::Search, "Nothing here").into_any_element()
+        }),
+        narrow_width(cx, "state-root", |_, _| {
+            ErrorView::not_found("missing").into_any_element()
+        }),
+        narrow_width(cx, "state-root", |_, _| {
+            ResultView::success("done", "Saved").into_any_element()
+        }),
+    ];
+    assert_eq!(
+        widths,
+        [px(240.0); 3],
+        "each view spans the card inside its padding"
+    );
+}
diff --git a/src/finance/depth.rs b/src/finance/depth.rs
index 0f72451..592d6b9 100644
--- a/src/finance/depth.rs
+++ b/src/finance/depth.rs
@@ -1,6 +1,6 @@
 use gpui::{
-    App, Div, ElementId, Entity, IntoElement, ParentElement, PathBuilder, Pixels, Point,
-    Refineable, RenderOnce, StyleRefinement, Styled, Window, canvas, div, fill,
+    App, Div, ElementId, Entity, InteractiveElement, IntoElement, ParentElement, PathBuilder,
+    Pixels, Point, Refineable, RenderOnce, StyleRefinement, Styled, Window, canvas, div, fill,
 };
 
 use super::quotes::moves;
@@ -250,7 +250,10 @@ impl RenderOnce for DepthChart {
         let (stroke, bottom) = (sizes.stroke.to_pixels(rem), frame.y + frame.h);
         let mark = reading.map(|(price, _, total)| (xs.at(price), ys.at(total)));
         let palette = colors.clone();
-        let mut root = div().relative().w_full().h(sizes.height);
+        let mut root = div()
+            .debug_selector(|| "chart-root".into())
+            .relative()
+            .h(sizes.height);
         root.style().refine(self.base.style());
         tracked(
             root,
diff --git a/src/finance/heatmap.rs b/src/finance/heatmap.rs
index d2514fc..205b6c4 100644
--- a/src/finance/heatmap.rs
+++ b/src/finance/heatmap.rs
@@ -165,7 +165,10 @@ impl RenderOnce for MarketHeatmap {
             theme.radius(Radius::Sm).to_pixels(rem),
             colors.fg,
         );
-        let mut root = div().relative().w_full().h(sizes.height);
+        let mut root = div()
+            .debug_selector(|| "chart-root".into())
+            .relative()
+            .h(sizes.height);
         root.style().refine(self.base.style());
         tracked(
             root,
diff --git a/src/finance/market.rs b/src/finance/market.rs
index e7d1bb9..455ac85 100644
--- a/src/finance/market.rs
+++ b/src/finance/market.rs
@@ -422,7 +422,10 @@ impl RenderOnce for CandlestickChart {
             },
         };
         let height = sizes.height + sizes.height * 0.3 * self.studies.len() as f32;
-        let mut root = div().relative().w_full().h(height);
+        let mut root = div()
+            .debug_selector(|| "chart-root".into())
+            .relative()
+            .h(height);
         root.style().refine(self.base.style());
         let steering = Steering {
             stage: stage.clone(),
diff --git a/src/finance/payoff.rs b/src/finance/payoff.rs
index af37260..9ff91dc 100644
--- a/src/finance/payoff.rs
+++ b/src/finance/payoff.rs
@@ -196,7 +196,9 @@ impl RenderOnce for PayoffDiagram {
         }
         chart.labels = labels;
         chart.format = Rc::new(|value| format::currency(value, "USD"));
-        let mut base = div().w_full().h(cx.theme().chart().height);
+        let mut base = div()
+            .debug_selector(|| "chart-root".into())
+            .h(cx.theme().chart().height);
         base.style().refine(self.base.style());
         plot(chart, base, window, cx)
     }
diff --git a/src/finance/renko.rs b/src/finance/renko.rs
index d46e736..e51457f 100644
--- a/src/finance/renko.rs
+++ b/src/finance/renko.rs
@@ -1,8 +1,8 @@
 use std::rc::Rc;
 
 use gpui::{
-    App, Div, ElementId, Entity, IntoElement, ParentElement, PathBuilder, Pixels, Refineable,
-    RenderOnce, StyleRefinement, Styled, Window, canvas, div, fill,
+    App, Div, ElementId, Entity, InteractiveElement, IntoElement, ParentElement, PathBuilder,
+    Pixels, Refineable, RenderOnce, StyleRefinement, Styled, Window, canvas, div, fill,
 };
 
 use jiff::tz::TimeZone;
@@ -146,7 +146,10 @@ fn board(
         theme.radius(crate::theme::Radius::Sm).to_pixels(rem),
     );
     let box_px = boxes.map(|size| (ys.at(0.0) - ys.at(size)).abs());
-    let mut root = div().relative().w_full().h(sizes.height);
+    let mut root = div()
+        .debug_selector(|| "chart-root".into())
+        .relative()
+        .h(sizes.height);
     root.style().refine(base.style());
     tracked(root, (id, "marks").into(), &tiles, move |place| {
         hit.iter().position(|(rect, _)| rect.contains(place))
diff --git a/src/finance/tests.rs b/src/finance/tests.rs
index 1e405a0..5a659c6 100644
--- a/src/finance/tests.rs
+++ b/src/finance/tests.rs
@@ -6,8 +6,11 @@ use gpui::{
 };
 use jiff::Timestamp;
 
-use crate::finance::{CandlestickChart, ChartSync, candles::Candle, stage::Visible};
-use crate::theme::Theme;
+use crate::finance::{
+    CandlestickChart, ChartSync, DepthChart, Leg, MarketHeatmap, PayoffDiagram, PointFigureChart,
+    RenkoChart, candles::Candle, stage::Visible,
+};
+use crate::{layout::tests::narrow_width, theme::Theme};
 
 fn candles(count: usize) -> Rc<Vec<Candle>> {
     Rc::new(
@@ -106,3 +109,41 @@ fn a_lagging_chart_leaves_the_shared_window_alone(cx: &mut TestAppContext) {
         "the lagging chart's append is already shown"
     );
 }
+
+#[gpui::test]
+fn every_chart_fills_a_column_its_block_measures_by_content(cx: &mut TestAppContext) {
+    cx.update(Theme::init);
+    let leg = Leg {
+        call: true,
+        strike: 100.0,
+        quantity: 1.0,
+        premium: 2.0,
+    };
+    let widths = [
+        narrow_width(cx, "chart-root", |_, _| {
+            DepthChart::new("depth", [(99.0, 2.0)], [(101.0, 3.0)]).into_any_element()
+        }),
+        narrow_width(cx, "chart-root", |_, _| {
+            MarketHeatmap::new("heatmap")
+                .tile("A", 1.0, 0.5)
+                .into_any_element()
+        }),
+        narrow_width(cx, "chart-root", |_, _| {
+            CandlestickChart::new("candles", candles(30)).into_any_element()
+        }),
+        narrow_width(cx, "chart-root", move |_, _| {
+            PayoffDiagram::new("payoff", [leg], (80.0, 120.0), 100.0).into_any_element()
+        }),
+        narrow_width(cx, "chart-root", |_, _| {
+            RenkoChart::new("renko", candles(30), 0.1).into_any_element()
+        }),
+        narrow_width(cx, "chart-root", |_, _| {
+            PointFigureChart::new("figure", candles(30), 0.1, 3).into_any_element()
+        }),
+    ];
+    assert_eq!(
+        widths,
+        [px(240.0); 6],
+        "each chart spans the card inside its padding"
+    );
+}
diff --git a/src/forms/checked.rs b/src/forms/checked.rs
index 7854617..3842ea5 100644
--- a/src/forms/checked.rs
+++ b/src/forms/checked.rs
@@ -43,10 +43,10 @@ fn checked(
     let theme = cx.theme();
     let (subtle, danger) = (theme.colors.fg_subtle, theme.colors.danger);
     div()
+        .debug_selector(|| "checked-root".into())
         .flex()
         .flex_col()
         .gap_1()
-        .w_full()
         .child(
             Input::new(state)
                 .size(size)
diff --git a/src/forms/mention.rs b/src/forms/mention.rs
index e1d682d..efd5e2e 100644
--- a/src/forms/mention.rs
+++ b/src/forms/mention.rs
@@ -172,9 +172,9 @@ impl Suggestions {
         let (up_rows, down_rows, enter_rows) = (rows.clone(), rows.clone(), rows.clone());
         let (enter, trigger) = (self.pick.clone(), self.trigger);
         div()
+            .debug_selector(|| "mention-root".into())
             .id(self.id)
             .relative()
-            .w_full()
             .capture_action(move |_: &Up, _, cx| {
                 if open {
                     cx.stop_propagation();
diff --git a/src/forms/number.rs b/src/forms/number.rs
index b67b8fd..6b9a67f 100644
--- a/src/forms/number.rs
+++ b/src/forms/number.rs
@@ -401,10 +401,10 @@ impl RenderOnce for NumberInput {
                     .child(stepper),
             );
         div()
+            .debug_selector(|| "number-root".into())
             .flex()
             .items_center()
             .gap_2()
-            .w_full()
             .children(label)
             .child(
                 div()
diff --git a/src/forms/select.rs b/src/forms/select.rs
index 3884000..804eb7e 100644
--- a/src/forms/select.rs
+++ b/src/forms/select.rs
@@ -88,13 +88,13 @@ pub(crate) fn field_button(
     let theme = cx.theme();
     let colors = &theme.colors;
     div()
+        .debug_selector(|| "field-root".into())
         .id(id)
         .track_focus(focus)
         .relative()
         .flex()
         .items_center()
         .gap_2()
-        .w_full()
         .h(theme.control_height(size))
         .px(theme.control_padding(size))
         .rounded(theme.radius(Radius::Md))
diff --git a/src/forms/slider.rs b/src/forms/slider.rs
index 1ee122f..7dc5770 100644
--- a/src/forms/slider.rs
+++ b/src/forms/slider.rs
@@ -243,13 +243,14 @@ impl Track {
                     })
             });
         div()
+            .debug_selector(|| "slider-root".into())
             .id(self.id)
             .flex_none()
             .map(|outer| {
                 if vertical {
                     outer.h_full().w(thumb).py(thumb * 0.5)
                 } else {
-                    outer.w_full().h(thumb).px(thumb * 0.5)
+                    outer.h(thumb).px(thumb * 0.5)
                 }
             })
             .when(self.disabled, |outer| outer.opacity(0.5))
diff --git a/src/forms/tests/choices.rs b/src/forms/tests/choices.rs
index 0e544ab..c93e506 100644
--- a/src/forms/tests/choices.rs
+++ b/src/forms/tests/choices.rs
@@ -67,14 +67,16 @@ struct Picker {
 impl Render for Picker {
     fn render(&mut self, _: &mut Window, cx: &mut Context<Self>) -> impl IntoElement {
         let view = cx.entity();
-        Select::new("select", abc(false))
-            .selected(self.chosen.clone())
-            .on_change(move |value, _, cx| {
-                view.update(cx, |view, cx| {
-                    view.chosen = value.clone();
-                    cx.notify();
-                })
-            })
+        div().size_full().child(
+            Select::new("select", abc(false))
+                .selected(self.chosen.clone())
+                .on_change(move |value, _, cx| {
+                    view.update(cx, |view, cx| {
+                        view.chosen = value.clone();
+                        cx.notify();
+                    })
+                }),
+        )
     }
 }
 
@@ -425,9 +427,11 @@ struct Empty(bool);
 
 impl Render for Empty {
     fn render(&mut self, _: &mut Window, _: &mut Context<Self>) -> impl IntoElement {
-        Select::new("empty", [])
-            .placeholder("Nothing yet")
-            .disabled(self.0)
+        div().size_full().child(
+            Select::new("empty", [])
+                .placeholder("Nothing yet")
+                .disabled(self.0),
+        )
     }
 }
 
diff --git a/src/forms/tests/dates.rs b/src/forms/tests/dates.rs
index 09ee490..4cd01f6 100644
--- a/src/forms/tests/dates.rs
+++ b/src/forms/tests/dates.rs
@@ -1,4 +1,7 @@
-use gpui::{Context, IntoElement, KeyUpEvent, Keystroke, Render, TestAppContext, Window};
+use gpui::{
+    Context, IntoElement, KeyUpEvent, Keystroke, ParentElement, Render, Styled, TestAppContext,
+    Window, div,
+};
 use jiff::civil::{Date, Time, date, time};
 
 use super::setup;
@@ -14,15 +17,17 @@ struct Day {
 impl Render for Day {
     fn render(&mut self, _: &mut Window, cx: &mut Context<Self>) -> impl IntoElement {
         let view = cx.entity();
-        DatePicker::new("day", self.value)
-            .today(TODAY)
-            .disabled(self.disabled)
-            .on_change(move |picked, _, cx| {
-                view.update(cx, |view, cx| {
-                    view.value = Some(picked);
-                    cx.notify();
-                })
-            })
+        div().size_full().child(
+            DatePicker::new("day", self.value)
+                .today(TODAY)
+                .disabled(self.disabled)
+                .on_change(move |picked, _, cx| {
+                    view.update(cx, |view, cx| {
+                        view.value = Some(picked);
+                        cx.notify();
+                    })
+                }),
+        )
     }
 }
 
@@ -48,14 +53,16 @@ struct Span {
 impl Render for Span {
     fn render(&mut self, _: &mut Window, cx: &mut Context<Self>) -> impl IntoElement {
         let view = cx.entity();
-        DateRangePicker::new("span", self.value)
-            .today(TODAY)
-            .on_change(move |picked, _, cx| {
-                view.update(cx, |view, cx| {
-                    view.value = Some(picked);
-                    cx.notify();
-                })
-            })
+        div().size_full().child(
+            DateRangePicker::new("span", self.value)
+                .today(TODAY)
+                .on_change(move |picked, _, cx| {
+                    view.update(cx, |view, cx| {
+                        view.value = Some(picked);
+                        cx.notify();
+                    })
+                }),
+        )
     }
 }
 
@@ -78,14 +85,18 @@ struct Clock {
 impl Render for Clock {
     fn render(&mut self, _: &mut Window, cx: &mut Context<Self>) -> impl IntoElement {
         let view = cx.entity();
-        TimePicker::new("clock", self.value)
-            .step(15)
-            .on_change(move |picked, _, cx| {
-                view.update(cx, |view, cx| {
-                    view.value = Some(picked);
-                    cx.notify();
-                })
-            })
+        div()
+            .size_full()
+            .child(
+                TimePicker::new("clock", self.value)
+                    .step(15)
+                    .on_change(move |picked, _, cx| {
+                        view.update(cx, |view, cx| {
+                            view.value = Some(picked);
+                            cx.notify();
+                        })
+                    }),
+            )
     }
 }
 
diff --git a/src/forms/tests/structure.rs b/src/forms/tests/structure.rs
index 5e53d1d..18722ba 100644
--- a/src/forms/tests/structure.rs
+++ b/src/forms/tests/structure.rs
@@ -1,12 +1,16 @@
 use gpui::{
-    AppContext as _, Context, Entity, InteractiveElement, IntoElement, KeyUpEvent, Keystroke,
+    App, AppContext as _, Context, Entity, InteractiveElement, IntoElement, KeyUpEvent, Keystroke,
     ParentElement, Render, Styled, TestAppContext, VisualTestContext, Window, div, px,
 };
 
 use super::setup;
 use crate::{
     buttons::Button,
-    forms::{FieldArray, Form, FormField, Input, InputEvent, TextInput},
+    forms::{
+        Choice, DatePicker, EmailInput, FieldArray, Form, FormField, Input, InputEvent,
+        MentionInput, NumberInput, Select, Slider, TextInput,
+    },
+    layout::tests::narrow_width,
 };
 
 struct Signup {
@@ -195,3 +199,35 @@ fn a_field_keeps_inside_its_cards_padding(cx: &mut TestAppContext) {
         "a percent min would take the card's outer width"
     );
 }
+
+#[gpui::test]
+fn fields_fill_a_column_their_block_measures_by_content(cx: &mut TestAppContext) {
+    setup(cx);
+    let field =
+        |window: &mut Window, cx: &mut App| window.use_keyed_state("field", cx, TextInput::new);
+    let widths = [
+        narrow_width(cx, "field-root", |_, _| {
+            Select::new("select", [Choice::new("a", "A")]).into_any_element()
+        }),
+        narrow_width(cx, "field-root", |_, _| {
+            DatePicker::new("date", None).into_any_element()
+        }),
+        narrow_width(cx, "checked-root", move |window, cx| {
+            EmailInput::new(&field(window, cx)).into_any_element()
+        }),
+        narrow_width(cx, "mention-root", move |window, cx| {
+            MentionInput::new("mention", &field(window, cx)).into_any_element()
+        }),
+        narrow_width(cx, "slider-root", |_, _| {
+            Slider::new("slider", 0.5).into_any_element()
+        }),
+        narrow_width(cx, "number-root", |_, _| {
+            NumberInput::new("number", 42.0).into_any_element()
+        }),
+    ];
+    assert_eq!(
+        widths,
+        [px(240.0); 6],
+        "each field spans the card inside its padding"
+    );
+}
diff --git a/src/layout/mod.rs b/src/layout/mod.rs
index 63da417..597c58c 100644
--- a/src/layout/mod.rs
+++ b/src/layout/mod.rs
@@ -12,6 +12,8 @@ mod sidebar;
 mod split;
 mod stack;
 mod surface;
+#[cfg(all(test, feature = "test-support"))]
+pub(crate) mod tests;
 mod viewport;
 mod workspace;
 
diff --git a/src/layout/tests.rs b/src/layout/tests.rs
new file mode 100644
index 0000000..ad223f6
--- /dev/null
+++ b/src/layout/tests.rs
@@ -0,0 +1,34 @@
+use gpui::{
+    AnyElement, App, Context, IntoElement, ParentElement, Pixels, Render, Styled, TestAppContext,
+    Window, div, px,
+};
+
+type Build = Box<dyn Fn(&mut Window, &mut App) -> AnyElement>;
+
+/// One element in a column that a padded block measures by content.
+struct Narrow(Build);
+
+impl Render for Narrow {
+    fn render(&mut self, window: &mut Window, cx: &mut Context<Self>) -> impl IntoElement {
+        div().w(px(280.0)).flex().flex_col().child(
+            div().p_5().child(
+                div()
+                    .flex()
+                    .flex_col()
+                    .child((self.0)(window, cx))
+                    .child("A line long enough to wrap in a narrow card, so the column fills it."),
+            ),
+        )
+    }
+}
+
+/// The width of `selector` in that column; a root that fills it takes all 240px.
+pub(crate) fn narrow_width(
+    cx: &mut TestAppContext,
+    selector: &'static str,
+    build: impl Fn(&mut Window, &mut App) -> AnyElement + 'static,
+) -> Pixels {
+    let (_, cx) = cx.add_window_view(|_, _| Narrow(Box::new(build)));
+    cx.run_until_parked();
+    cx.debug_bounds(selector).expect(selector).size.width
+}
diff --git a/src/navigation/steps.rs b/src/navigation/steps.rs
index 8236777..da5a6f1 100644
--- a/src/navigation/steps.rs
+++ b/src/navigation/steps.rs
@@ -200,10 +200,10 @@ impl RenderOnce for Steps {
             }
         });
         div()
+            .debug_selector(|| "steps-root".into())
             .id(self.id)
             .flex()
             .when(vertical, |steps| steps.flex_col())
-            .w_full()
             .children(steps)
     }
 }
diff --git a/src/navigation/tests.rs b/src/navigation/tests.rs
index 05927ba..88a678b 100644
--- a/src/navigation/tests.rs
+++ b/src/navigation/tests.rs
@@ -6,10 +6,11 @@ use gpui::{
 
 use super::{
     BackForwardNavigation, Breadcrumb, Crumb, EditorTab, EditorTabs, GoToLine, LoadMore,
-    NavigationMenu, Tabs, Wizard,
+    NavigationMenu, Steps, Tabs, Wizard,
 };
 use crate::{
     forms::{Choice, TextInput},
+    layout::tests::narrow_width,
     theme::Theme,
 };
 
@@ -456,3 +457,16 @@ fn load_more_asks_once_per_press_and_goes_once_all_show(cx: &mut TestAppContext)
         "all shown, no button"
     );
 }
+
+#[gpui::test]
+fn steps_fill_a_column_their_block_measures_by_content(cx: &mut TestAppContext) {
+    setup(cx);
+    let width = narrow_width(cx, "steps-root", |_, _| {
+        Steps::new("steps", [Choice::new("a", "A"), Choice::new("b", "B")], 0).into_any_element()
+    });
+    assert_eq!(
+        width,
+        px(240.0),
+        "the steps span the card inside its padding"
+    );
+}