Quote from that SO post: "This is not a Safari bug. It's just a different interpretation of the spec.
When dealing with percentage heights, some browsers (like Safari) adhere to the traditional interpretation of the spec, which requires a defined height on the parent.
In other words, a percentage height on an in-flow element will be recognized only when the parent has a defined height.
Some browsers, such as Chrome and Firefox, have moved past this interpretation and now accept flex and grid heights as an adequate parent reference for a child with a percentage height.
But Safari is stuck in the past. This doesn't mean it's wrong, invalid or a bug."
Just worth noting, as I had a lot of fun with that one.
https://caniuse.com/?search=grid