it'd be nice to have a similar button to remove from game
The main reason there isn't a remove button is so that you can fit more players there without having to scroll. You can remove players by dragging them back to the left side.
Double-click functionality on menus like where you chose custom, my theme, built-in theme
Good idea - I didn't think of that. I'll add it to my list for the next update (but it may be a while.)
it feels like that grey theme should be more prevalent on the site
Yeah, the plan is to integrate it everywhere. Other pages will get facelifts too and eventually everything will be consistent.