[Dark Theme] Make everything dark

[Slddev]

This can cause a lot of bugs, so I'm doing this slowly 😄.

• [ ] Set background of the whole page to dark.
• [ ] Set every single text white.
• [ ] Check every single page for any bugs.

File manager and login cannot be darkmode sadly. This is due to the fact that the Design override doesn't support them yet.

[Slddev]

Busy right now... Postponing this.