This is from the old school of thought on the web, the HTML is only about content and semantics, and all the typography should be left to the browser (and user preferences). If the default font in your browser causes fatigue for you, you can change the defaults. This is hardly possible with most websites now without intrusive browser extensions.
Works on any screen, desk, mobile. Works in Lynx from the command line.
Just narrow your window, maybe by changing the width of your sidebar.
Typography is an art way more ancient than computers and I feel that it should be taken into account even on webpages; famously, Donald Knuth studied typography pretty deeply when designing TeX.