🐛 Add close button to responsive menu sidebar

[pranay911]

Description

Adds a close button (×) inside the amp-sidebar component in the responsive menu example to improve user experience. Previously, users could only close the sidebar by clicking the hamburger button again, which wasn't intuitive. Now there's a dedicated, clearly visible close button inside the sidebar.

Changes

• Added close button with × symbol inside the amp-sidebar element
• Positioned absolutely at top-right corner with proper styling
• Button uses on="tap:sidebar.close" to close the sidebar
• Added CSS styling for better visibility:
  • White background with border and shadow for contrast
  • Hover states for better UX
  • Focus outline for accessibility
  • Proper z-index to ensure visibility above content
• Added padding-top to sidebar to prevent content overlap with close button

Testing

• Tested locally at http://localhost:8000/examples/responsive-menu.amp.html
• Verified button appears correctly in the top-right corner of the sidebar
• Verified button closes the sidebar when clicked
• Verified button is visible and accessible with proper styling
• Tested on responsive viewport sizes

Screenshots