Irene Vlachou is a typeface designer specialising in Greek and variable fonts working between Bristol, UK, and Athens, Greece. For her personal website, she’s using Recursive (Mono Casual style) as variable font.
On hover, the link with the IPA pronunciation changes from bold (weight 700) to regular italic (weight 400, slant –15) via the CSS property font-variation-settings. Thanks to the fixed width, there is no text reflow.