[feature] Add custom CSS for Instance Frontpage

[S0yKaf]

Is your feature request related to a problem ?

You're able to add custom CSS for individual profiles but not for the instance front page itself.

Describe the solution you'd like.

Implement a custom CSS field in the instance settings that works the same way as the custom CSS for profiles but that affects the front page.

This would also change the CSS for the /about and /signup page or any other instance related pages. Excluding the dashboard

Describe alternatives you've considered.

Instance admins could potentially do this by manually editing the provided CSS files. However, it's not everyone who's comfortable doing this. and a built-in setting would be more fun and accessible.

Additional context.

No response

[tsmethurst]

Oh weird I could have sworn we had an issue open for this already. Thanks!