Dark email body content
Dark theme works great except that the message body content is set to have a white background of "#fff". An easy fix is the following:
1.) Apply a CSS filter. "filter: invert(1)" to the element with attribute data-testid="message-content:body"
2.) Apply another CSS filter to images so they are not inverted. CSS selector img.
I tried it and it works but it's not permanent since I'm only modifying the styles using the browser's dev tools.
Please add this to the dark theme CSS.
Ryūga Hideki commented
This should be a priority because it's indeed a bug in all the dark themes. It makes it really difficult to use them when required due to the fact that the entire e-mail is indeed a bright contrast with the overall interface.