[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
bezier-curve grid issues:
* too dark on light theme - color should be same as top/bottom of gradient so grid fades away
* too large on dark theme - there are 10 grid lines in original (light theme) grid, but only 7.5 in dark theme grid. Size appears to be 20x20, but should be 15x15