Revert "Add dark mode"

[Aloso]

Revert "Add dark mode"

This reverts commit 6ad1467.

Fixes #1096

[Aloso]

Explanation:

The CSS in newsletters is inlined automatically. However, this doesn't work for rules in @media blocks, so they stay in the <style> tag and end up having a lower specificity than everything else.

This could be solved by adding !important to every rule in @media blocks. I'd be happy to do this if that's okay.

[nasa42]

I wonder if adding !important would have any side effects, e.g., if the dark mode is always the picked theme. Worth trying if you're willing to! 👍

[Aloso]

@nasa42 adding !important within a @media block doesn't have side effects. If the dark theme is disabled or unsupported, the @media block is ignored entirely.