grid-definition-{rows|columns} allows the grid breadth to be sized after a minmax function: <track-minmax> => minmax( <track-breadth> , <track-breadth> ) | auto | <track-breadth> <track-breadth> => <length> | <percentage> | <fraction> | min-content | max-content Currently we only support <length> | <percentage>.
*** Bug 104125 has been marked as a duplicate of this bug. ***
Relevant comment from the duplicated bug (https://bugs.webkit.org/show_bug.cgi?id=104125#c2): (In reply to comment #1) > The spec says min-content and max-content. We already support -webkit-min-content and -webkit-max-content for things like height and width. > > I suspect what we should do is add min-content and max-content support for places where we already support -webkit-min-content and -webkit-max-content and only support min-content and max-content for grid. Then we can someday drop support for the -webkit prefix versions. We discussed this further with Tony and agreed to use the existing prefixed version, under the contract that we should also unprefix them when we unprefix grid.
The minmax() support was added some time ago in different bugs like bug 104700 or bug 108403 (there are some others too)