Do you mean you want a bigger Icon on the select?
if so you can use this css
.ui-btn-icon-left:after, .ui-btn-icon-right:after, .ui-btn-icon-top:after, .ui-btn-icon-bottom:after, .ui-btn-icon-notext:after #selectNavType {
margin-top:-14px;
width: 28px;
height: 28px;
}