That’s fine. It’s just a tick in Firefox to do so. Yesterday I made a readme intended for some Windows friends. Just a simple single html page. I set it to “Segoe UI”,sans-serif so it looks more like a Windows manual. If someone opens it on a mobile device or a Mac somehow, then it still looks fine. It mostly just avoids people seeing Times New Roman or Arial, which I don’t need A/B testing for to know is not as nice to look at or doesn’t look very Windows like.
Unless you use Chrome, you can also go to the reader mode to avoid all the CSS. Plenty of options for you!