stretch now exists as a keyword for width/height.
The stretch keyword is a keyword for use with CSS sizing properties (such as width and height) that lets elements grow to exactly fill their containing block's available space.
It’s similar to 100%, except the resulting size is applied to the margin box of the element instead of the box determined by box-sizing.
This lets the element take up the available space without overflowing, especially when margins or padding are in use.
box-sizing: border-box works around padding and border, but it doesn't work around margin (as it's outside of the border in the box model). stretch works on a level above that, and thus fixes all three. Similar to how [[flexbox]] works.
https://css-tricks.com/we-completely-missed-width-height-stretch/