> just style both at the same time
That's exactly the point. The system by default sets both colors, though most browsers I've used allow the website to override the colors. In these cases, the websites only override one but not the other.
You're using the word "override"; what do you think the order of these things is? As far as I'm aware:
- The user sets their system's colours (e.g. for me that's white text and black background). These are used by all applications, including the browser.
- Web sites may override these defaults by providing CSS, e.g. Google dictionary forcing the text to be black
These bugs are caused by Facebook, Dropbox, Google, Twitter, etc. shipping broken overrides. It's a pretty minor problem (as this post's author acknowledges), but it's not the user's fault.
If these sites didn't try to override things, i.e. by providing plain, semantic HTML, then this problem wouldn't occur (some might prefer such sites!)
I agree, but I think this could be phrased better: If the system is using a (light-foreground-on-)dark-background theme, it should force web pages to use a dark-background theme, no matter what CSS they have.