How to theme the scrollbar in xtermjs?

If anyone is looking, this was my solution in the xterm.css addind --webkit onto the viewport selector

.xterm .xterm-viewport {
  /* On OS X this is required in order for the scroll bar to appear fully opaque */
  background-color: transparent;
  overflow-y: scroll;
  cursor: default;
  position: absolute;
  right: 0;
  left: 0;
  top: 0;
  bottom: 0;
  scrollbar-color: var(--highlight) var(--dark);
  scrollbar-width: thin;
}

.xterm-viewport::-webkit-scrollbar {
  background-color: var(--dark);
  width: 5px;
}

.xterm-viewport::-webkit-scrollbar-thumb {
  background: var(--highlight);
}