Add a dark mode option

[planetoftheweb]

Related to #3

Add a dark mode option to the site.

• index.html:

  • Add a button in the menu to toggle light and dark mode with id="theme-toggle".

• script.js:

  • Add a script to handle the toggling between light and dark mode.
  • Add an event listener to the theme-toggle button to toggle the data-theme attribute on the html element.

• style.css:

  • Add styles for dark mode using the [data-theme="dark"] attribute selector.

• README.md:

  • Update the README file to include the dark mode feature.

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For more details, open the Copilot Workspace session.