lucky for you it's finally in the CSS draft proposal now https://drafts.csswg.org/css-sizing-4/#ratios https://drafts.csswg.org/css-sizing-4/#ratios you can us

lucky for you it's finally in the CSS draft proposal now https://drafts.csswg.org/css-sizing-4/#ratios https://drafts.csswg.org/css-sizing-4/#ratios you can use it in all major browsers except Safari