Adding a switch for change themes

[Ritwik880]

Is your feature request related to a problem? Please describe.
Dark Mode is a supplemental mode that can be used to display mostly dark surfaces on the UI. The design reduces the light emitted by device screens while maintaining the minimum color contrast ratios required for readability.
Additionally, it conserves battery power.

[TheComputerM]

This can already be done using CSS variables, how do you propose to implement this.

[lukaszpolowczyk]

Definitely in the first place, docs should support css prefers-color-scheme.
That is, as it is in Mozilla Docs - a button consisting of three options:

[benmccann]

closing since the site has been rewritten. please file at https://github.com/sveltejs/svelte.dev/issues/new if the issue persists