Hide the top bar on the home page

Visitors see the home page with no top bar at all. Signed in, the bar
sits behind a small tab at the top center that drops it down; Escape or
a click outside closes it. Every other page keeps the regular bar.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

web/static/css/app.css

@@ -67,6 +67,28 @@ code { font: 0.9em ui-monospace, SFMono-Regular, Menlo, Consolas, monospace; bac
 .topnav-form { margin: 0; }
 @media (max-width: 520px) { .topnav a span { display: none; } }
 
+/* Home page, signed in: the bar drops down from a small tab. */
+.topbar-tab {
+  position: fixed; top: 0; left: 50%; z-index: 30; transform: translateX(-50%);
+  display: grid; place-items: center; width: 44px; height: 20px;
+  list-style: none; cursor: pointer; color: var(--faint);
+  background: color-mix(in srgb, var(--surface) 88%, transparent);
+  border: 1px solid var(--border); border-top: 0; border-radius: 0 0 10px 10px;
+  backdrop-filter: blur(10px); -webkit-backdrop-filter: blur(10px);
+  opacity: 0.7; transition: opacity 0.15s, color 0.15s, top 0.2s;
+}
+.topbar-tab::-webkit-details-marker { display: none; }
+.topbar-tab .icon { width: 14px; height: 14px; transition: transform 0.2s; }
+.topbar-tab:hover, .topbar-tab:focus-visible { opacity: 1; color: var(--text); }
+.topbar-tab:focus-visible { outline: 2px solid var(--accent); outline-offset: 2px; }
+.topbar-drawer .topbar { position: fixed; left: 0; right: 0; animation: topbar-drop 0.2s ease-out; }
+.topbar-drawer[open] .topbar-tab { top: 60px; opacity: 1; }
+.topbar-drawer[open] .topbar-tab .icon { transform: rotate(180deg); }
+@keyframes topbar-drop { from { transform: translateY(-100%); } }
+@media (prefers-reduced-motion: reduce) {
+  .topbar-drawer .topbar { animation: none; }
+}
+
 /* ---------- footer ---------- */
 .footer { margin-top: 72px; border-top: 1px solid var(--border); color: var(--faint); font-size: 13px; }
 .footer-inner { display: flex; flex-wrap: wrap; gap: 8px; justify-content: center; padding-top: 22px; padding-bottom: 28px; }

web/static/js/common.js

@@ -189,3 +189,16 @@ document.addEventListener("click", (e) => {
     if (!d.contains(e.target) || e.target.closest(".menu-pop a")) d.open = false;
   }
 });
+
+// The home page's drop-down top bar closes on Escape or a click outside it.
+document.addEventListener("click", (e) => {
+  const d = document.querySelector("details.topbar-drawer[open]");
+  if (d && !d.contains(e.target)) d.open = false;
+});
+document.addEventListener("keydown", (e) => {
+  const d = document.querySelector("details.topbar-drawer[open]");
+  if (e.key === "Escape" && d) {
+    d.open = false;
+    d.querySelector("summary").focus();
+  }
+});