Ignoring XML based languages (XSL, PGML), some of the early ones, that never made it to browsers, were DSSSL and FOSI. There was also JSS (JavaScript Style Shee

Ignoring XML based languages (XSL, PGML), some of the early ones, that never made it to browsers, were DSSSL and FOSI. There was also JSS (JavaScript Style Sheets, 1996). Mobile app development (e.g. Flutter) have their own APIs for styling, but they're still quite similar to CSS. There might be other languages used in areas I'm not familiar with.