Hey, another site that was built on a Mac and not tested on anything else.

So, Avenir Next is not a system font on Windows or Linux. On Windows, this means you get the browser's default stylesheet fallback, which means Times New Roman. So your site essentially looks like a Word 97 document to all your Windows visitors, and who-knows-what on the various Linux distros.

Take a look at https://css-tricks.com/snippets/css/system-font-stack/ https://www.smashingmagazine.com/2015/11/using-system-ui-fon... and get yourself looking correct for those non-macOS users!

What did you use to build that stylesheet? A framework of some sort?