Like Night and Day
I famously can't read dark themes on a PC — that is, thin light text overwhelmed by a dark background.
I've tried various fixes, including a bookmarklet and Stylus for Firefox, but I just found the most counterintuitive and easiest fix yet. The Firefox add-on “Dark Background and Light Text,” despite its name, is fully configurable to do the opposite by swapping the background and foreground colors and making link text a little darker. The icon can be pinned to the toolbar and easily be switched on and off as needed.
I hope this helps other people with vision sensitivity. You can find this recommended add-on at https://addons.mozilla.org/en-US/firefox/addon/dark-background-light-text/
(I'm using it now: it's the only way I can read this blog!) 😀