A great start – now the synchronisation just needs to be a bit smarter:
border-top-width: 10px;
border-top-style: solid;
border-top-color: var(–secondary);
border-right-width: 10px;
border-right-style: solid;
border-right-color: var(–secondary);
border-bottom-width: 10px;
border-bottom-style: solid;
border-bottom-color: var(–secondary);
border-left-width: 10px;
border-left-style: solid;
border-left-color: var(–secondary);
(sync from controls to css panel)
how about:
border: 10px solid var(–secondary);