The font-synthesis CSS property controls whether user agents are allowed to synthesize oblique, bold and small-caps font faces when a font family lacks oblique, bold and small-caps faces, respectively.
Without font-synthesis property some web pages that do not have font families with the required variations may have unnatural forms of fonts due to synthesis. This feature has 17⭐️ on the bugtracker #509989 and has been requested by designers. Firefox and Safari have already implemented this feature.
Samples: https://drafts.csswg.org/css-fonts-4/#font-synthesis-intro
Explainers: https://drafts.csswg.org/css-fonts-4/#font-synthesis-intro https://developer.mozilla.org/en-US/docs/Web/CSS/font-synthesis