Overlapping CSS flexbox items in Safari

The element is shrinking. You need to set the flex-shrink property to 0 on the shrinking element.

main >div:first-child {
  -webkit-flex: 0;
  flex-shrink: 0;
}

While I can no longer replicate the issue of OP using Safari 14.0.2, I still observe in some cases where Safari would over-shrink elements that other browsers like Safari and Firefox do not.

Although setting flex-shrink: 0; works, in some cases, we intend to use like flex: 0 1 15% where we want shrinking to happen, but without the over-shrinking.

Workaround seems to work for me:

min-height: min-content (or min-width)

I also had a similar issue where flex box direction changed to column overlapped items on iPad. The issue was with the flex: 0 1 0; property applied to child element. Give the base value auto. flex: 0 1 auto;

.parent{
    display: flex;
    flex-direction: column;
}
.parent .child{
    flex: 0 1 auto;
}