If you stick to text files, you'll never have to go to caniuse.com ever. Need styles? Just make a PDF and throw that online. During the "XML HTML" phase the web went through, I never had to worry about validating my PDFs through an XML validator. Then when everyone decided using "<b>" and "<font>" tags was bad and insisting we switch to using "font-weight" CSS in a completely unrelated part of the file, guess what I had to do? Nothing! My PDF keeps rendering exactly the same way through every silly "trend" and "update" on the web, and never misses a beat on Lighthouse in Chrome.
Now if I could just convince all the browsers to implement .docx renderers out of the box, I'd really be set.