tweak(ui): group edited files list styling

packages/ui/src/components/session-review.css

@@ -68,7 +68,7 @@
   [data-slot="session-review-diffs-group"] {
     background-color: var(--background-stronger);
     border-radius: var(--radius-lg);
-    box-shadow: var(--shadow-xs-border-base);
+    border: 1px solid var(--border-weak-base);
     overflow: clip;
 
     [data-component="accordion"] {

packages/ui/src/components/session-turn.css

@@ -127,7 +127,49 @@
     padding-top: 8px;
     display: flex;
     flex-direction: column;
-    gap: 12px;
+  }
+
+  [data-slot="session-turn-diffs-group"] {
+    background-color: var(--background-stronger);
+    border-radius: var(--radius-lg);
+    border: 1px solid var(--border-weak-base);
+    overflow: clip;
+
+    [data-component="accordion"] {
+      gap: 0;
+    }
+
+    [data-component="accordion"]
+      [data-slot="accordion-item"]
+      [data-slot="accordion-header"]
+      [data-slot="accordion-trigger"] {
+      border: 0;
+      border-radius: 0;
+      box-shadow: none;
+      background-color: transparent;
+
+      &:hover {
+        background-color: var(--surface-base-hover);
+      }
+
+      &:active {
+        background-color: var(--surface-base-active);
+      }
+    }
+
+    [data-component="accordion"]
+      [data-slot="accordion-item"]
+      + [data-slot="accordion-item"]
+      [data-slot="accordion-header"]
+      [data-slot="accordion-trigger"] {
+      border-top: 1px solid var(--border-weak-base);
+    }
+
+    [data-component="accordion"] [data-slot="accordion-item"][data-expanded] [data-slot="accordion-content"] {
+      border: 0;
+      border-top: 1px solid var(--border-weak-base);
+      border-radius: 0;
+    }
   }
 
   [data-slot="session-turn-diff-trigger"] {

packages/ui/src/components/session-turn.tsx

@@ -315,6 +315,7 @@ export function SessionTurn(
                       <Collapsible.Content>
                         <Show when={open()}>
                           <div data-component="session-turn-diffs-content">
+                            <div data-slot="session-turn-diffs-group">
                               <Accordion
                                 multiple
                                 value={expanded()}
@@ -386,6 +387,7 @@ export function SessionTurn(
                                 </For>
                               </Accordion>
                             </div>
+                          </div>
                         </Show>
                       </Collapsible.Content>
                     </Collapsible>