Created attachment 324819 [details] Test to reproduce the issue This is easily reproducible if you combine "height: -webkit-fill-avilable" with "box-sizing: border-box" and the element has some border and/or padding. Attached example to reproduce the issue. And current output, the expected result would be that both cyan boxes (the one with "content-box" and the one with "border-box") take the whole height of their wrapper. BTW this is working fine in Chromium/Blink.
Created attachment 324820 [details] Current output
This was fixed past year in Blink: https://codereview.chromium.org/2100463002/
Fixed in - https://chromium.googlesource.com/chromium/src/+/4820bd94507b69754af99a83b26a1cdcd936d134