I can pretty much always read sites that don't bother to override the browser defaults, whereas people's CSS efforts often make things hard to read. It's obvio

I can pretty much always read sites that don't bother to override the browser defaults, whereas people's CSS efforts often make things hard to read. It's obviously possible to make sites nicer using CSS, but if you're just trying to let people read your words rather than show off your design skills, leaving it to the browser's defaults is absolutely fine.