Improve UI: capitalize publications title and make visitor map collapsible

- Change 'selected publications' to 'Selected Publications'
- Make visitor map collapsible with 🌍 Visitor Map summary
- Reduce visual prominence while maintaining functionality
- Better user experience with optional map viewing

Author: Keyu-He

_layouts/about.liquid

@@ -59,7 +59,7 @@ layout: default
     <!-- Selected papers -->
     {% if page.selected_papers %}
       <h2>
-        <a href="{{ '/publications/' | relative_url }}" style="color: inherit">selected publications</a>
+        <a href="{{ '/publications/' | relative_url }}" style="color: inherit">Selected Publications</a>
       </h2>
       {% include selected_papers.liquid %}
     {% endif %}
@@ -75,11 +75,15 @@ layout: default
 
     <!-- Visitor Map -->
     {% if site.visitor_map.enabled %}
-      <div class="visitor-map" style="text-align: center; margin-top: 2rem;">
-        <h2>visitor map</h2>
-        <div id="visitor-map-widget">
-          <script type="text/javascript" id="mapmyvisitors" src="//mapmyvisitors.com/map.js?d=VGq-6ngx9SQOzI4uqqrGzo8741s606-66KR_dTZ9b00&cl=ffffff&w=a"></script>
-        </div>
+      <div class="visitor-map" style="margin-top: 1.5rem;">
+        <details style="text-align: center;">
+          <summary style="cursor: pointer; font-size: 1.1rem; color: #666; margin-bottom: 1rem;">
+            🌍 Visitor Map
+          </summary>
+          <div id="visitor-map-widget" style="margin-top: 1rem; opacity: 0.9;">
+            <script type="text/javascript" id="mapmyvisitors" src="//mapmyvisitors.com/map.js?d=VGq-6ngx9SQOzI4uqqrGzo8741s606-66KR_dTZ9b00&cl=ffffff&w=a"></script>
+          </div>
+        </details>
       </div>
     {% endif %}