I found stylus to work really well for this.. I have most of my apps typically in Nord palette. For some frequently visited websites, such as HN, I apply the Nord theme. Not sure if it was already built by someone else, but something I found chatbots are quite good at is creating custom CSS! I point it at a website and ask for a Nord themed customs CSS. Copy Paste into Stylus... most sites I tried it oneshotted a very decent solution.