diff --git a/lib/features/assistant/assistant_page_state_closure.dart b/lib/features/assistant/assistant_page_state_closure.dart
index 5b48d330..6c82337c 100644
--- a/lib/features/assistant/assistant_page_state_closure.dart
+++ b/lib/features/assistant/assistant_page_state_closure.dart
@@ -268,6 +268,7 @@ extension AssistantPageStateClosureInternal on AssistantPageStateInternal {
   }) {
     return LayoutBuilder(
       builder: (context, constraints) {
+        final palette = context.palette;
         final maxPaneWidth = math.min(
           560.0,
           math.max(
@@ -282,22 +283,25 @@ extension AssistantPageStateClosureInternal on AssistantPageStateInternal {
           children: [
             Expanded(child: child),
             if (!artifactPaneCollapsedInternal) ...[
-              SizedBox(
-                key: const Key('assistant-artifact-pane-resize-handle'),
-                width: assistantHorizontalResizeHandleWidthInternal,
-                child: PaneResizeHandle(
-                  axis: Axis.horizontal,
-                  onDelta: (delta) {
-                    setState(() {
-                      artifactPaneWidthInternal =
-                          (artifactPaneWidthInternal - delta)
-                              .clamp(
-                                assistantArtifactPaneMinWidthInternal,
-                                maxPaneWidth,
-                              )
-                              .toDouble();
-                    });
-                  },
+              DecoratedBox(
+                decoration: BoxDecoration(color: palette.chromeBackground),
+                child: SizedBox(
+                  key: const Key('assistant-artifact-pane-resize-handle'),
+                  width: assistantHorizontalResizeHandleWidthInternal,
+                  child: PaneResizeHandle(
+                    axis: Axis.horizontal,
+                    onDelta: (delta) {
+                      setState(() {
+                        artifactPaneWidthInternal =
+                            (artifactPaneWidthInternal - delta)
+                                .clamp(
+                                  assistantArtifactPaneMinWidthInternal,
+                                  maxPaneWidth,
+                                )
+                                .toDouble();
+                      });
+                    },
+                  ),
                 ),
               ),
               const SizedBox(width: assistantHorizontalPaneGapInternal),
diff --git a/lib/theme/app_theme.dart b/lib/theme/app_theme.dart
index 4b24a91b..28973eb3 100644
--- a/lib/theme/app_theme.dart
+++ b/lib/theme/app_theme.dart
@@ -21,13 +21,13 @@ class SimpleSpacing {
 class SimpleRadius {
   SimpleRadius._();
 
-  static const double card = 16.0;
+  static const double card = 12.0;
   static const double button = 12.0;
-  static const double input = 14.0;
+  static const double input = 12.0;
   static const double chip = 12.0;
   static const double badge = 12.0;
-  static const double dialog = 18.0;
-  static const double sidebar = 20.0;
+  static const double dialog = 12.0;
+  static const double sidebar = 12.0;
   static const double icon = 12.0;
 }
 
diff --git a/lib/web/web_assistant_page_core.dart b/lib/web/web_assistant_page_core.dart
index cec8dfab..4d6eab25 100644
--- a/lib/web/web_assistant_page_core.dart
+++ b/lib/web/web_assistant_page_core.dart
@@ -372,6 +372,7 @@ class WebAssistantPageStateInternal extends State<WebAssistantPage> {
   }) {
     return LayoutBuilder(
       builder: (context, constraints) {
+        final palette = context.palette;
         final maxPaneWidth = math.min(
           520.0,
           math.max(
@@ -386,22 +387,25 @@ class WebAssistantPageStateInternal extends State<WebAssistantPage> {
           children: [
             Expanded(child: child),
             if (!artifactPaneCollapsedInternal) ...[
-              SizedBox(
-                key: const Key('assistant-artifact-pane-resize-handle'),
-                width: 8,
-                child: PaneResizeHandle(
-                  axis: Axis.horizontal,
-                  onDelta: (delta) {
-                    setState(() {
-                      artifactPaneWidthInternal =
-                          (artifactPaneWidthInternal - delta)
-                              .clamp(
-                                webAssistantArtifactPaneMinWidthInternal,
-                                maxPaneWidth,
-                              )
-                              .toDouble();
-                    });
-                  },
+              DecoratedBox(
+                decoration: BoxDecoration(color: palette.chromeBackground),
+                child: SizedBox(
+                  key: const Key('assistant-artifact-pane-resize-handle'),
+                  width: 8,
+                  child: PaneResizeHandle(
+                    axis: Axis.horizontal,
+                    onDelta: (delta) {
+                      setState(() {
+                        artifactPaneWidthInternal =
+                            (artifactPaneWidthInternal - delta)
+                                .clamp(
+                                  webAssistantArtifactPaneMinWidthInternal,
+                                  maxPaneWidth,
+                                )
+                                .toDouble();
+                      });
+                    },
+                  ),
                 ),
               ),
               const SizedBox(width: 8),
diff --git a/test/theme/app_theme_suite.dart b/test/theme/app_theme_suite.dart
index aa6d19a9..83dbc221 100644
--- a/test/theme/app_theme_suite.dart
+++ b/test/theme/app_theme_suite.dart
@@ -38,9 +38,9 @@ void main() {
   });
 
   test('AppTheme matches calm compact workspace baseline tokens', () {
-    expect(AppRadius.card, 16);
-    expect(AppRadius.input, 14);
-    expect(AppRadius.dialog, 18);
+    expect(AppRadius.card, 12);
+    expect(AppRadius.input, 12);
+    expect(AppRadius.dialog, 12);
     expect(AppRadius.chip, 12);
     expect(AppTypography.sectionSize, 13);
     expect(AppTypography.bodySize, 13);