I'm sorry if this has been addressed somewhere else.  Searches for backgrounds always go to the character feature.  Searches for visual settings always go to icons for statuses and the like.  I recently purchased Xanathar's Guide to Everything and The Monster Manual on this website and had instant buyer's regret.  Don't worry this isn't a post about me wanting my money back.  The highlighted words that give you condition and spell descriptions are wonderful, but the black text on the bright white background strains my eyes badly.  I was hoping there might be a possibility of changing the website background to brown or yellowish paper color.  I'd even accept white text on a black background.  I understand this feature isn't a priority, but it would really mean a lot to me and there is probably at least one other person on the sit who gets eye strain from reading on a computer.

Black text on a white background is like literally the standard for displaying written text...? How do you use the rest of the internet? Or even new books? 

   Well, those are fair questions.  The book doesn't apply, because it's not a screen.  I'm not an ophthalmologist and I don't know what is about screens that strains some people's eyes when they read on them.  I just know that if I read too long on a computer it starts to hurt my eyes.  Bright white screens are the worst, which makes some sense, because that is when the screen is emitting the maximum amount of light.  As for the rest of the internet.  I'm fine in short bursts, but I like to sit down and read the D&D books for a few hours at a time.

   As for the dark mode.  That looks like exactly what I'm looking for.  Here's hoping it comes to PC as well.

I would certainly support options like you suggest. In the meantime, have you tried blue light filtering glasses?  They are made for those who experience problems looking at screens for lengthy periods. I've not tried them, but my daughter has and they have really helped her. 

Thanks.  I'll look into those.