Does anybody knows if it is possible to use cascating stylesheets in ComboBoxes or ListBoxes ?

I have a file where i put all my definitions called styles.css , and i have created a definition for listboxes like this

.List
{
Background-color : #ffffff;
border-bottom: #000060 2px solid;
border-top: #000060 2px solid;
border-left: #000060 2px solid;
border-right: #000060 2px solid;
.........
}

but it doesn't work . It works for inputs and textareas , but it doesn't work for combos .

Can anyone help me?

Thanks in advanced