fix: enhance table of contents visual hierarchy with custom CSS

- Added distinct bullet styles (disc for main, circle for sub-items)
- Implemented proper indentation with padding and margins
- Added subtle left border for nested sections using theme color
- Differentiated font sizes between main sections and subsections
- Improved line height and spacing for better readability
- Maintains PicoCSS compatibility while clearly showing hierarchy

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

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

index.html

@@ -18,6 +18,31 @@
         max-width: 960px;
         margin: 0 auto;
     }
+    
+    /* Table of Contents Visual Hierarchy */
+    aside nav ul {
+        list-style-type: disc;
+        padding-left: 20px;
+    }
+    
+    aside nav ul ul {
+        list-style-type: circle;
+        padding-left: 30px;
+        margin-top: 8px;
+        border-left: 2px solid rgba(67, 160, 71, 0.2);
+        padding-left: 20px;
+        margin-left: 10px;
+    }
+    
+    aside nav li {
+        margin: 6px 0;
+        line-height: 1.4;
+    }
+    
+    aside nav ul ul li {
+        margin: 4px 0;
+        font-size: 0.9em;
+    }
     </style>
 
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