block · almmaasoglu · Jul 21, 2026
@@ -243,9 +243,17 @@ export function AppSidebar({
   const showSidebarUpdateCard =
     canShowSidebarUpdateCard && !isSidebarUpdateCardDismissed;
   const [dmActionsMenuOpen, setDmActionsMenuOpen] = React.useState(false);
+  const [hasScrolledFromTop, setHasScrolledFromTop] = React.useState(false);
   const scrollRef = React.useRef<HTMLDivElement>(null);
   useSidebarScrollLock(scrollRef);
 
+  const handleSidebarScroll = React.useCallback(
+    (event: React.UIEvent<HTMLDivElement>) => {
+      setHasScrolledFromTop(event.currentTarget.scrollTop > 0);
+    },
+    [],
+  );
+
   React.useEffect(() => {
     const scrollElement = scrollRef.current;
     if (!scrollElement) return;
@@ -549,6 +557,7 @@ export function AppSidebar({
     <Sidebar
       className="!border-r-0"
       collapsible="offcanvas"
+      data-scrolled-from-top={hasScrolledFromTop}
       data-testid="app-sidebar"
       variant="sidebar"
     >
@@ -585,6 +594,7 @@ export function AppSidebar({
 
           <SidebarContent
             className="buzz-sidebar-scrollbar overscroll-none"
+            onScroll={handleSidebarScroll}
             ref={scrollRef}
           >
             <div

@@ -37,9 +37,15 @@
     bottom: calc(var(--buzz-sidebar-edge-fade-size) * -1);
     height: var(--buzz-sidebar-edge-fade-size);
     left: 0;
+    opacity: 0;
     right: 0;
   }
 
+  [data-testid="app-sidebar"][data-scrolled-from-top="true"]
+    [data-testid="sidebar-pinned-header"]::before {
+    opacity: 1;
+  }
+
   [data-testid="app-sidebar"] [data-sidebar="footer"]::before {
     background: linear-gradient(
       to top,

@@ -22,6 +22,54 @@ async function storedSidebarWidth(page: Page) {
   );
 }
 
+async function topEdgeFadeOpacity(page: Page) {
+  return page
+    .getByTestId("sidebar-pinned-header")
+    .evaluate((element) => getComputedStyle(element, "::before").opacity);
+}
+
+async function expectTopEdgeFadeTracksSidebarScroll(page: Page) {
+  const scroller = page
+    .getByTestId("app-sidebar")
+    .locator('[data-sidebar="content"]');
+  const pinnedHeader = page.getByTestId("sidebar-pinned-header");
+  const inbox = page
+    .getByTestId("sidebar-primary-menu")
+    .getByRole("button", { name: "Inbox" });
+  const scrollContent = page.getByTestId("sidebar-scroll-content");
+
+  await expect(scroller).toBeVisible();
+  await expect(inbox).toBeVisible();
+  const [headerBottom, inboxTop] = await Promise.all([
+    pinnedHeader.evaluate((element) => element.getBoundingClientRect().bottom),
+    inbox.evaluate((element) => element.getBoundingClientRect().top),
+  ]);
+  expect(inboxTop).toBeCloseTo(headerBottom);
+  await expect(scrollContent).toHaveCSS("padding-top", "0px");
+  await expect.poll(() => topEdgeFadeOpacity(page)).toBe("0");
+
+  await scroller.evaluate((element) => {
+    element.scrollTop = 24;
+  });
+  await expect
+    .poll(() => scroller.evaluate((element) => element.scrollTop))
+    .toBeGreaterThan(0);
+  await expect.poll(() => topEdgeFadeOpacity(page)).toBe("1");
+
+  await scroller.evaluate((element) => {
+    element.scrollTop = 0;
+  });
+  await expect
+    .poll(() => scroller.evaluate((element) => element.scrollTop))
+    .toBe(0);
+  await expect.poll(() => topEdgeFadeOpacity(page)).toBe("0");
+  await expect
+    .poll(() =>
+      inbox.evaluate((element) => element.getBoundingClientRect().top),
+    )
+    .toBeCloseTo(headerBottom);
+}
+
 // Regression guard for the "Leave channel" lockup: with two bundled copies of
 // @radix-ui/react-dismissable-layer, opening a modal AlertDialog from a modal
 // Radix ContextMenu left `pointer-events: none` stuck on <body> after the
@@ -324,6 +372,19 @@ test("fades the pinned sidebar chrome edges outside the Buzz theme", async ({
   expect(fadeStyles.footerZIndex).toBe("5");
   expect(fadeStyles.channelBeforeBackground).toBe("none");
   expect(fadeStyles.channelAfterBackground).toBe("none");
+
+  await expectTopEdgeFadeTracksSidebarScroll(page);
+});
+
+test("shows the dark-theme header fade only after the sidebar scrolls", async ({
+  page,
+}) => {
+  await page.addInitScript(() => {
+    window.localStorage.setItem("buzz-theme", "github-dark");
+  });
+  await page.goto("/");
+
+  await expectTopEdgeFadeTracksSidebarScroll(page);
 });
 
 test("aligns the sidebar search with the channel title outside the Buzz theme", async ({