Theme change doesn't work perfectly whilst widget is open. #140
Description
Screen.Recording.2023-05-31.at.16.51.00.mov
Re-opening or doing something to the plot seems to fix.
Discussion in #138 (comment)_ and ff.
Also maybe related: when @dstansby switches to light theme, the background of the widget is not updated. At the moment I can't reproduce this. Separate comment in: #138 (comment)
