Add Media Queries for Dark/Light Mode

## Description
Add **dark and light theme support** using CSS media queries or classes.

### Requirements
- Theme should switch based on system preference (`prefers-color-scheme`) or CSS class toggle.
- Ensure all existing components look good in both themes.
- HTML & CSS only.

### File/Folder
- css/dark-light.css
- components/* (update any components as needed)

### Example/Screenshot
- Optional: Include screenshots showing light and dark modes.