I used to use system fonts for my blog theme, but I rethought this decision and converted to the following font-family in my CSS:

font-family: sans-serif;

Right, that’s just sans-serif. This should choose the default sans serif font, which is configurable in most browsers.

By choosing sans-serif only, I give the reader the option to decide for themselves which font to choose. If I use the system fonts, I ignore the user’s preferences and force a specific font on them, which they may not have set as default for good reasons.

And also browser developers will surely have thought about which font is set by default. In my Flatpak-Firefox on Ubuntu, for example, “DejaVu Sans” is set by default and I think it doesn’t look too bad.