When using fixed pixels flex-basis on an element with flex-direction: row which is wrapped within a flex box, the flex-basis value behaves as max-height for that element, no matter what it's child is. Test case: https://codepen.io/saltas888/pen/wvBRRoP Work-around: Use width instead of flex-basis
<rdar://problem/58825822>
I am unable to reproduce this issue in Safari 16.1 using CodePen from Comment 0 and it shows "blue" container in height similar to section child matching in rendering with other browsers (Chrome Canary 109 and Firefox Nightly 108). Since all browsers are matching with each other, I am marking this as "RESOLVED CONFIGURATION CHANGED" assuming it is fixed along the way. Please reopen with updated testcase, if it is still reproducible. Thanks!