feat(css): Styled scrollbars in Firefox Nightly (#8653)

You currently need to enable `layout.css.scrollbar-colors.enabled` in `about:config` in Firefox
Nightly.

Closes: #32
1 job for pleroma in 4 minutes and 9 seconds (queued for 8 seconds)
Status Job ID Name Coverage
  Test
passed #8308
build

00:04:09