[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
This problem is caused by this line: https://github.com/adobe/brackets/pull/8529/files#diff-6abceb212a7a54f2c4bbb656b6c646f6R189 which is not properly scoped to the inline editor.