On some epub devices, you can change the background color to black, with the font switching to white. My iBook program allows four distinct styles.
Is there a way to override these styles for particular elements? For example, I'm converting a book that's in the public domain to an epub. I'm adding a few notes, which I style (red text) to indicate those notes were written by me, not the original author.
But if I switch to dark mode, my styles are lost. If I insert a style directly into my text, like this...
<span style="color: #f00;">Make me yellow!</span>
...even that is overriden.
P.S. There is at least one workaround of sorts. Device styles don't appear to affect border colors. If I style a paragraph with a red border, for example, then the border remains red when I preview my epub. I haven't tested it in all devices, however.