I want change css default:
.z-combobox-rounded-pp .z-comboitem-over,
.z-combobox-pp .z-comboitem-over {
background: #363636;
}

.z-combobox-rounded-pp .z-comboitem-over-seld,
.z-combobox-pp .z-comboitem-over-seld {
background: #363636;
}

to

.myStyle.z-combobox-rounded-pp .z-comboitem-over,
.myStyle.z-combobox-pp .z-comboitem-over {
background: #363636;
}

.myStyle.z-combobox-rounded-pp .z-comboitem-over-seld,
.myStyle.z-combobox-pp .z-comboitem-over-seld {
background: #363636;
}

not works ?