If you dislike the new default colors, just go to theme settings and select "photon classic"
This new update allows instance admins to set their own themes (via PUBLIC_THEME) and allows you to have multiple theme presets.
It's available on phtn.app right now, coming soon to a release
Seems that there's still some time to be spent fiddling with CSS layouts.
*removed externally hosted image*
But anyway, this is an awesome update.