tree_sytle_tab.css

/* hightlight selected tab */
tab-item.active tab-item-substance {
  height: 39px !important;
}
tab-item.active .background {
  background-color: steelblue;
}
tab-item.active .label-content {
  font-weight: bold;
  font-size: 14px;
}
tab-item.active tab-twisty,
tab-item.active .label-content,
tab-item.active tab-counter {
  color: #fff;
}

/* hightlight specific domain */
tab-item[data-current-uri^="https://github.com"] tab-item-substance {
  background: #415640;
}
tab-item[data-current-uri^="https://github.com"]:hover tab-item-substance {
  background: #415690;
}

/* Only show tab close button on hover */
#tabbar tab-item tab-item-substance:not(:hover) tab-closebox {
  display: none;
}

:root.sidebar #background {
  background: ;
}

#tabbar { scrollbar-width: auto; }