Poor behaviour for nojs users

[Sobeston]

Current problems with javascript disabled:

• light/dark switcher doesn't work, nor does it respect prefers-color-scheme.
• tab items (e.g. "windows" on the installation page) aren't usable at all, you're stuck on the default tab.

If it's possible to rework the theme so that it works with javascript disabled without breaking the light/dark toggle button, that would be great. I'm sure it's possible to use pure html for the correct tab item behaviour. If this can't be fixed, some warning for nojs users would be helpful