dynamic width custom select box with CSS

Question

I need to style the select boxes in my web site something like below,

I have suceded with html+css for fix sizes as below,

<div><select></select></div>

div{
    background: url("select-box-background.png") no-repeat scroll right center #fff;
    height: 23px;
    overflow: hidden;
    width: 54px;
}
select{
    background: transparent;
    border: 0 none;
    border-radius: 0;
    font-size: 12px;
    line-height: 1;
    padding: 3px;
    width: 78px;
    color: #78abd0;
}

But I can't manage to apply this for all select boxes with different width, because I have done the styles with fix width.

How to manage same thing with the dynamic width.