Fix navigation scroll - make entire header scrollable

Changed approach: make the entire header fixed and scrollable instead of just the nav section. This provides better UX and avoids layout conflicts.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <[email protected]>

Author: DavidLiedle

assets/css/custom.css

@@ -16,19 +16,12 @@ footer {
   padding-top: 20px;
   border-top: 1px solid #e5e5e5;
   margin-bottom: 20px;
-  max-height: 600px;
-  overflow-y: auto;
 }
 
 .book-nav h2 {
   font-size: 18px;
   margin-bottom: 10px;
   color: #333;
-  position: sticky;
-  top: 0;
-  background: white;
-  padding: 5px 0;
-  z-index: 10;
 }
 
 .book-nav ul {
@@ -101,6 +94,27 @@ blockquote {
   margin: 0 0 16px 0;
 }
 
+/* Desktop: Make header fixed with scrollable nav */
+@media screen and (min-width: 961px) {
+  header {
+    position: fixed;
+    width: 270px;
+    overflow-y: auto;
+    height: 100vh;
+    padding-bottom: 50px;
+  }
+
+  section {
+    margin-left: 300px;
+  }
+
+  footer {
+    position: fixed;
+    bottom: 0;
+    width: 270px;
+  }
+}
+
 /* Mobile responsiveness */
 @media screen and (max-width: 960px) {
   .book-nav {