Update web/index.html

web/index.html

@@ -2078,15 +2078,31 @@
     if (e.key === 'theme') applyTheme(e.newValue);
   });
 
+  var overlay = document.getElementById('theme-overlay');
+  if (!overlay) {
+    overlay = document.createElement('div');
+    overlay.id = 'theme-overlay';
+    overlay.style.cssText = [
+      'position:fixed','inset:0','z-index:99999',
+      'pointer-events:none','opacity:0',
+      'transition:opacity 0.18s ease','background:#fff'
+    ].join(';');
+    document.body.appendChild(overlay);
+  }
+
   function switchTheme() {
     var darkTheme = document.getElementById('darkTheme');
     if (!darkTheme) return;
-    var newTheme = darkTheme.disabled ? 'dark' : 'light';
-    applyTheme(newTheme);
-    localStorage.setItem('theme', newTheme);
-    if (typeof updateChartData === 'function') {
-        updateChartData(7);
-    }
+    var goingDark = darkTheme.disabled;
+    overlay.style.background = goingDark ? '#fff' : '#1a1a2e';
+    overlay.style.opacity = '1';
+    setTimeout(function () {
+      var newTheme = goingDark ? 'dark' : 'light';
+      applyTheme(newTheme);
+      localStorage.setItem('theme', newTheme);
+      if (typeof updateChartData === 'function') updateChartData(7);
+      setTimeout(function () { overlay.style.opacity = '0'; }, 50);
+    }, 180);
   }
 
   document.addEventListener('DOMContentLoaded', function () {