Extends the CSS sizing properties with keywords that represent content-based "intrinsic" sizes and context-based "extrinsic" sizes, allowing CSS to more easily describe boxes that fit their content or fit into a particular layout context. (Note that the "fill" keyword is only shipping prefixed so far, pending CSSWG agreement to unprefix)
Docs: https://developer.mozilla.org/en-US/docs/Web/CSS/width https://developer.mozilla.org/en-US/docs/Web/CSS/height
Samples: https://googlechrome.github.io/samples/css-intrinsic-sizing/index.html