gtk-combobox.css

/* Combobox settings */
combobox {
   padding: 1px;
   background-color: @base_color;
   border-color: @borders;
   border: 1px solid @dark_shadow;
   border-bottom: 1px solid @light_shadow;
   border-right: 1px solid @light_shadow;
   border-radius: 0px;
   box-shadow: 1px 1px @borders inset, -1px -1px @theme_bg_color inset; }

combobox :checked {
   padding: 1px;
   border-color: @borders;
   border: 1px solid @dark_shadow;
   border-bottom: 1px solid @light_shadow;
   border-right: 1px solid @light_shadow;
   border-radius: 0px;
   box-shadow: 1px 1px @borders inset, -1px -1px @theme_bg_color inset; }

combobox:disabled {
   background-color: @bg_color;
}

combobox cellview, combobox cellview:focus, combobox cellview:checked,
combobox cellview:active, combobox cellview:hover {
   background-color: transparent;
   padding: 0px;
   margin-top: -2px;
   margin-bottom: -2px; }

combobox button:checked box {
   margin: 0;
   margin-left: -4px;
   margin-top: 2px;
   margin-right: -4px;
   margin-bottom: 2px; }

combobox > box {
   margin: -2px; }

combobox button:checked box {
   margin: -1px;
   margin-left: -2px; }