Change 'select' highlight color [duplicate]

Answer 1

In Firefox, the default stylesheet is

option:checked {
    background-color: -moz-html-cellhighlight !important;
    color: -moz-html-cellhighlighttext !important;
}

The problem is that you can't override an internal important property, even if you use !important.

So, basically, you can't, unless you implement your own UI.

Edit: On some browsers, you can use a box-shadow trick.