https://www.w3.org/TR/CSS22/visudet.html#min-max-heights <percentage> Specifies a percentage for determining the used value. The percentage is calculated with respect to the height of the generated box's containing block. If the height of the containing block is not specified explicitly (i.e., it depends on content height), and this element is not absolutely positioned, the percentage value is treated as '0' (for 'min-height') or 'none' (for 'max-height').
Created attachment 349103 [details] Patch
Committed r235773: <https://trac.webkit.org/changeset/235773>
<rdar://problem/44207968>