@Ronnie old post, I just saw it. I think I've seen you say you use an iPad, is that correct?
If you are using Safari on iPad, there are a couple of apps/extensions you can install that let you run custom CSS (Cascading Style Sheets) for websites. I have not used these, but your question was interesting, as I do use custom CSS on my desktop Safari for a couple sites, so thought I'd google on it for iPad.
Unfortunately, it's not as simple on iPad as loading a custom stylesheet via Safari preferences on desktop. But these apps/extensions appear to make it possible:
1. Makeover - Custom CSS
2. Userscripts
Both available in the App Store, both free and claim no user data tracking.
What I'm unclear on is if you have to initialize them for each use. In my custom stylesheets on the desktop, the class or ID names are unique enough for websites that they suffice for limiting the restyling to those sites.
If you're interested in trying this route, I could investigate them a bit further, test and if it seems to be a viable solution, write some custom styles you could paste into your installation.