Here is a reduced test case: https://jsbin.com/debujav/edit?html,css,output The button displays properly in Chrome, but in Safari the background disappears. If you remove or change the properties, for instance, setting display: inline-block or border-color: rgba(0, 0, 0, 0.01) the background appears.
This bug occurs in Safari 15.4, but we are able to confirm it does not happen in 15.2
<rdar://problem/92705832>
*** This bug has been marked as a duplicate of bug 238088 ***