https://drafts.csswg.org/css-sizing-3/#valdef-width-fit-content-length-percentage now introduces a fit-content(<length-percentage>) value, that is a new value similar to fit-content, except taking an argument instead of using the available width. This seems worth implementing, particularly given how easy it should be to implement. (It's not a particularly high priority.)
Did we implement this as part of CSS Grid? Because this demo is working: https://codepen.io/jensimmons/pen/QpZpWR?editors=1100 I think. And I think it works in Safari / aka, Igalia's implementation.
Oh, maybe this ticket is for implementing `fit-content` outside of a Grid container context. Sorry to clutter it up with confusion. I would appreciate a double-check that it is implemented to be used with Grid, because MDN implies otherwise. https://developer.mozilla.org/en-US/docs/Web/CSS/fit-content