More customizable UI colors and fonts

[johnchoi313]

Light and dark default UI modes for Cards/ButtonPanels/Prompts are great, but it would be great to have an option to customize these further to have a more unique style in certain scenes. In particular, it would be great to customize font colors, border colors, and main body colors, as well as font styles if possible.

(Requested by ARENA-ETC team.)

[hi-liang]

This should be fully resolved clientside as the args just get passed through from arena-py args as documented in arenaxr/arena-web-core#617

Leaving this to close out by @johnchoi313 if that is sufficient explanation