would be cool if it supported basic html/css

That's the approach I used for my thermal printer based project. Render HTML/CSS to B/W Image and then print it on the thermal printer.

https://sales-and-dungeons.app/

An easy way to do this, which I use to print recipes with my TP, is to render the page as an image. I use dom-to-image for that.

I can print webpages straight to my Epson TM-T20IV. My web browser just sends it to CUPS.