static/themes/metro/combobox.css

.combobox-item,
.combobox-group {
  font-size: 12px;
  padding: 3px;
  padding-right: 0px;
}
.combobox-item-disabled {
  opacity: 0.5;
  filter: alpha(opacity=50);
}
.combobox-gitem {
  padding-left: 10px;
}
.combobox-group {
  font-weight: bold;
}
.combobox-item-hover {
  background-color: #E6E6E6;
  color: #444;
}
.combobox-item-selected {
  background-color: #CCE6FF;
  color: #000;
}