Does anyone know how to do multiple properties for the same value in Garden? I searched but couldn't find the right keywords to use maybe

.display-flex {
    display: -webkit-flex;
    display: flex;
}

Just use multiple maps.

{:display :-webkit-flex} {:display :flex}

Also, in your case, using vendor prefixes may also solve the problem: https://github.com/noprompt/garden/blob/master/ChangeLog.md#compiler-flag-changes