Bug 208201

In Safari, a CSS grid container with position fixed or absolute does not correctly handle the 1fr unit vertically.

Minimal repro: https://www.scirra.com/labs/bugs/safarigrid.html

The CSS grid container is positioned to fill the entire screen. It has four cells, with columns and rows 100px 1fr.

Expected result: entire screen to be green, since it is covered by the four cells.
Observed result: lower part of the screen is red (the CSS grid container), since it is not covered by the bottom two cells.

The 1fr unit fills the container horizontally, but not vertically. The lower two cells incorrectly compute a height of 0px.

It works correctly in Chrome, Firefox, and (legacy) Edge. It also seems works correctly in Safari with static or relative positioning on the container; only the fixed/absolute positioning is broken.