Flexbox children collapse in Safari but not in other browsers. Here is the minimal example (JSFiddle):
<html>
<body style="display: flex;height: 100vh;flex-flow: column;">
<div style="display: flex;background: red;">
<div style="padding: 1rem;">test</div>
</div>
<div style="height: 1000rem;"></div>
</body>
</html>
Here we have a div with red background wrapping another div with some padding. There is also another flex child that is very tall (1000rem).
In Chrome or Firefox the result looks normal. The red flex child wraps its own child properly:
Now in Safari it looks completely wrong (tested on Version 14.0.2 (16610.3.7.1.9)) - the second tall child causes the first one to collapse:
The red child got collapsed despite having a child. It looks like the default min-height: auto that is applied by the browser is being ignored in Safari.
Is there a workaround to make Safari behave according to the spec?

