Style the recording window

The five colors cover the background, a secondary background, the text, the secondary text, and the border. Leaving any of them unset falls back to the standard light or dark theme, so you override only what you actually want to change. A separate matching toggle keeps the recording window's button gradient in sync with the floating button and hides those individual controls while it is on. Clicking the preview bubble opens a mock window, so you can see all the colors together before saving anything.