override default selector style

gistfile1.css

/*  month / year expiry stuff    */
.select {
    height: 24px;
    border: 1px solid #ccc;
    border-top: 1px solid #888;
    padding: 0px 0 0 0px;
    background: url(https://www.poundpay.com/images/dropdown.png) no-repeat right #fff;
    -webkit-appearance: none;
    -moz-appearance: none;
    overflow: hidden;
    border-radius: 0;
    display: block;
    float:left;
}
select {
    background: transparent;
    border: 0;
    -webkit-appearance: none;
    -moz-appearance: none;
    width: 100px;
    padding: 4px 0 5px 8px;
    text-align: left;
    font-size: 12px;
    position: relative;
    top: -1px;
    &:focus {
        //outline: 0;
    }
}
#expiration {
    padding-right: 10px;

    .month.select {
        width: 42px;
        margin-right: 8px;
        
        &.disabled {
            background-color: #eee;
            select {
               color: #333;
            }
        }
    }
    .year.select {
        width: 65px;
        
        &.disabled {
            background-color: #eee;
            color: #333;
            select {
               color: #333;
            }
        }
    }
    .month.select select {
        padding-left: 5px;
    }
}
@-moz-document url-prefix() {
   #expiration .month.select select { padding-left: 0; }
   #expiration .year.select select { padding-left: 5px; }
}

@dblock: dug up this code from our payments iframe that we used to provide. We did it this way to keep the selectors consistent with the look and feel of the input fields. Use as you please.