Match style of config with site

[blankdvth]

Currently, the default styling for the GM_config is used, which is a) light theme (ew) and b) clashing with the site theme. GM_config can be styled using CSS, so it would be ideal to match it with the site theme (or at least make it a dark theme). This applies to the Forums Enhancement only, as MAUL is currently still a light theme.

Here's some wiki documentation for reference:
https://github.com/sizzlemctwizzle/GM_config/wiki/#customizing-gm_config
https://github.com/sizzlemctwizzle/GM_config/wiki/FAQ#why-is-gm_config-so-ugly
https://github.com/sizzlemctwizzle/GM_config/wiki/FAQ#how-do-i-change-the-style-of-the-frame