Hi

I tried like this (changed to int to make it even simpler)

QTreeWidget#activeCalls::item[isTalking="0"]{
background: green;
}

QTreeWidget#activeCalls::item[isTalking="1"]{
background: yellow;
}

in the code I simple call setIsTalking(0) or setIsTalking(1)

Still no action at all though.