Don't show highlight rectangle on button press

[Tim Curtis]

I'll add to panels :-)

Code:

.btn {
-webkit-tap-highlight-color: rgba(0, 0, 0, 0);
-webkit-user-select: none;
-webkit-touch-callout: none;
}

.btn:active {color:var(--textvariant);} /* this needs to be a separate rule */