Additional CSS warns about invalid CSS, though it's perfectly valid

[ZanderZ]

Add the following to Customize -> Additional CSS:

.foo {
    display: grid;
    gap: 0.25em;
    grid-gap: 0.25em;
    grid-template-columns: repeat(4, 1fr);
}

WordPress will give an error that the CSS is invalid (Expected RBRACE at the position of 1fr) and gives a warning that gap and grid-gap are "Unknown property"s.
All of this is perfectly fine CSS and WordPress should not give an error/warning about this.

[ZanderZ]

Proof of the error and warning

[pento]

Thank you for the bug report, @ZanderZ! We're tracking this issue over on #44471.

[ZanderZ]

Ah thanks, my search for duplicate tickets didn't find that one apparently.