font-family: Verdana, Geneva, sans-serif;

My computer has neither Verdana nor Geneva, and my browser's default sans-serif is Noto Sans, which has bars on the upper case "I".

Verdana does, too. It looks like Geneva does not (<http://www.identifont.com/show?1O3>), so you're probably using Geneva.

Maybe Verdana is the default for Windows, Geneva for MacOS, and "other" for Linuxes.