first attempt

banner.js

@@ -51,15 +51,64 @@
     }
   `;
 
+  // Jellyfin's own nav chrome has moved before (left drawer -> top app bar in
+  // 12.x) and will likely move again. Rather than hardcoding selectors that
+  // break on every redesign, find whatever is fixed/sticky and anchored near
+  // the top of the viewport at runtime, and push it down (Y) by the banner's
+  // height so the banner never just sits in front of (Z) live nav chrome.
+  const originalMarginTop = new WeakMap();
+  const offsetElements = new Set();
+
+  function isTopBarCandidate(el) {
+    if (el.id === BANNER_ID || el.closest('#' + BANNER_ID)) return false;
+    const style = getComputedStyle(el);
+    if (style.position !== 'fixed' && style.position !== 'sticky') return false;
+    if (style.display === 'none' || style.visibility === 'hidden' || parseFloat(style.opacity) === 0) return false;
+    const rect = el.getBoundingClientRect();
+    if (rect.width < window.innerWidth * 0.5) return false;    // must span most of the viewport width
+    if (rect.height <= 0 || rect.height > window.innerHeight * 0.6) return false; // skip full-page overlays/modals
+    if (rect.top > 400) return false;                          // must be anchored near the top of the page
+    return true;
+  }
+
+  function findTopBars() {
+    return Array.prototype.filter.call(document.body.querySelectorAll('*'), isTopBarCandidate);
+  }
+
+  function pushDownTopBars(offsetPx) {
+    const candidates = new Set(findTopBars());
+
+    // Restore anything we previously offset that's no longer a candidate
+    // (e.g. replaced by the SPA router on navigation).
+    offsetElements.forEach(function (el) {
+      if (!candidates.has(el) || !document.contains(el)) {
+        if (originalMarginTop.has(el)) {
+          el.style.marginTop = originalMarginTop.get(el);
+        }
+        offsetElements.delete(el);
+      }
+    });
+
+    candidates.forEach(function (el) {
+      if (!originalMarginTop.has(el)) {
+        originalMarginTop.set(el, el.style.marginTop || '');
+      }
+      const base = originalMarginTop.get(el);
+      el.style.marginTop = offsetPx > 0
+        ? 'calc(' + (base || '0px') + ' + ' + offsetPx + 'px)'
+        : base;
+      offsetElements.add(el);
+    });
+
+    if (offsetPx > 0 && candidates.size === 0) {
+      console.warn('[custom-banner] No fixed top navigation elements detected to push down; banner may overlap the menu.');
+    }
+  }
+
   function applyOffset() {
     const banner = document.getElementById(BANNER_ID);
-    const offset = banner ? (banner.offsetHeight + 'px') : '';
-    const header = document.querySelector('.headerTop');
-    const drawer = document.querySelector('.mainDrawer');
-    const sections = document.querySelector('.homeSectionsContainer');
-    if (header) header.style.marginTop = offset;
-    if (drawer) drawer.style.marginTop = offset;
-    if (sections) sections.style.marginTop = offset;
+    const offset = banner ? banner.offsetHeight : 0;
+    pushDownTopBars(offset);
   }
 
   function isHomePage() {
@@ -101,15 +150,27 @@
   style.textContent = BANNER_CSS;
   document.head.appendChild(style);
 
-  // React to SPA navigation
-  window.addEventListener('hashchange', update);
-
-  // Watch for Jellyfin's deferred body rendering (SPA bootstraps after DOMContentLoaded)
-  // subtree: true catches .headerTop wherever it appears in the DOM
-  const observer = new MutationObserver(function () {
+  // Debounce: the SPA's own DOM churn (list virtualization, image loads, etc.)
+  // can fire many mutations per second. We don't need per-frame precision for
+  // nav-bar layout, so coalesce bursts instead of rescanning the whole DOM
+  // on every single mutation.
+  let debounceTimer = null;
+  function scheduleUpdate(delay) {
+    clearTimeout(debounceTimer);
+    debounceTimer = setTimeout(function () {
       update();
       applyOffset();
-  });
+    }, delay || 150);
+  }
+
+  // React to SPA navigation
+  window.addEventListener('hashchange', update);
+  window.addEventListener('resize', function () { scheduleUpdate(); });
+
+  // Watch for Jellyfin's deferred body rendering (SPA bootstraps after
+  // DOMContentLoaded) and re-run on DOM churn, since the nav bar can be
+  // unmounted/remounted by the SPA router.
+  const observer = new MutationObserver(function () { scheduleUpdate(); });
   document.addEventListener('DOMContentLoaded', function () {
     observer.observe(document.body, { childList: true, subtree: true });
     update();