diff --git a/crates/core/src/alert.rs b/crates/core/src/alert.rs
index 8b2d19b..57eb08c 100644
--- a/crates/core/src/alert.rs
+++ b/crates/core/src/alert.rs
@@ -126,7 +126,13 @@ impl RenderOnce for Alert {
         let muted_foreground = theme.colors.muted_foreground;
         let muted = theme.colors.muted;
         let surface = theme.colors.surface;
-        let border = theme.colors.border;
+
+        let border = if theme.borders.overlays {
+            theme.colors.border
+        } else {
+            surface
+        };
+
         let shadows = theme.elevations.popover.shadows();
         let metrics = theme.sizes.resolve(Size::Medium);
         let icon_size = metrics.icon_size;
@@ -190,7 +196,7 @@ impl RenderOnce for Alert {
                         .id((self.id, "alert-close"))
                         .flex_none()
                         .cursor_pointer()
-                        .p_0p5()
+                        .p_1()
                         .rounded(theme.radius.sm)
                         .hover(|style| style.bg(muted))
                         .child(
diff --git a/docs/CHECKLIST.md b/docs/CHECKLIST.md
index 41ce6e9..1192583 100644
--- a/docs/CHECKLIST.md
+++ b/docs/CHECKLIST.md
@@ -14,7 +14,6 @@ is the first downstream consumer; its screens drive the order.
 Platform metric adoption continues one component at a time; each stop goes
 through the review gate and a gallery pass.
 
-- [ ] **Alert platform chrome** — overlay border gate.
 - [ ] **Combobox platform chrome** — popup border behind
       `Theme::borders.overlays`; the trigger follows the input stop's field
       treatment.
@@ -127,6 +126,10 @@ Gaps surfaced by the signed comparison; ordered by signed's usage.
       it flips above the parent when it would overflow the window bottom
       (the panel records its own height after the first frame); unanchored
       tooltips fall back to the cursor-offset wrapper
+- [x] Alert platform chrome — the banner border behind
+      `Theme::borders.overlays` (and dark mode), taking the surface color
+      where the platform paints none; it rides the popover elevation, so
+      dark mode's no-shadow rule applies to it too
 - [x] Button, Checkbox, Switch, Radio + RadioGroup, Toggle, Link, Slider,
       Progress, Avatar (image + seeded pixel-art fallback)
 - [x] Spinner — painted ring + rotating-icon variant, indeterminate and