CSS - alternate color for listbox and dropdownlist

dear friends

any idea of how to make alternate color for listbox and dropdownlist thru CSS. my web project is running thru vs2005 C#

.list {
font-family: Arial;
font-size: 12px;
font-weight:normal;
background-color: #FFFFCC;
color: black;
}

.dropdownlist
{
font-family: Arial;
font-size: 12px;
font-weight:normal;
background-color: #FFFFCC;
color: black;
}