[REVIEW ONLY] Dark UI theme for inline editors

This is a spinoff of @larz0's work in #8362 with a goal of fixing #8379.

As of this initial push, I have done inline CSS and color editors. The timing editor is almost done, and quick docs remains.

cc @MiguelCastillo
I thought about keeping the light grid but they pop out too much on a dark background and it's hard to see transparent colors that way because the brightness grabs all the attention.