I find the default darkmode background to be a sort of cool black (rgb(25,25,25)), which is probably a me thing, but in case anyone else is running into that, I restyled them:
* {
--color-notBlack: #222222;
}
article[data-theme="dark"].co-themed-box .co-post-box,
[data-theme="dark"].co-themed-box.co-post-box,
[data-theme="dark"].co-themed-box .co-post-box .co-editable-body,
[data-theme="dark"].co-themed-box.co-post-box .co-editable-body {
background-color: var(--color-notBlack);
}
I used #222222, which is the same color I use everywhere. It is the perfect gray for me. You can use whatever you like. I have doubtless missed something, but...well, there it is.
