feat: add dynamic green highlighting for bottom scroll and zoom controls

- Add green background (#27ae60) to info and back-to-top buttons when at page bottom
- Implement bottom detection (within 50px threshold) in scroll handler
- Add conditional green hover to zoom reset button (only when zoom ≠ 100%)
- Enhance UX with visual feedback for scroll position and zoom state

static/css/main.css

@@ -2601,6 +2601,11 @@ html {
     background: #3a3a3a;
 }
 
+.back-to-top.at-bottom {
+    opacity: 1;
+    background: #27ae60;
+}
+
 .back-to-top:active {
     transform: translateY(-1px);
     box-shadow: 0 3px 10px rgba(0, 0, 0, 0.3);
@@ -2647,6 +2652,11 @@ html {
     background: #3a3a3a;
 }
 
+.info-button.at-bottom {
+    opacity: 1;
+    background: #27ae60;
+}
+
 .info-button:active {
     transform: translateY(-1px);
     box-shadow: 0 3px 10px rgba(0, 0, 0, 0.3);
@@ -3661,6 +3671,13 @@ html {
     color: white;
 }
 
+/* Green hover only when zoom is not at default (100) */
+.zoom-reset-btn.zoom-not-default:hover {
+    background: rgba(39, 174, 96, 0.5);
+    border-color: rgba(39, 174, 96, 0.5);
+    color: rgba(255, 255, 255, 0.5);
+}
+
 .zoom-reset-btn:active {
     transform: scale(0.95);
 }