span.ui-datepicker-trigger {
    width: 16px;
    height: 16px;
    background: url("../jquery.ui.datepicker.jalali/themes/base/images/icon-calendar.svg") 0 0 no-repeat;
    margin-top: auto;
    margin-bottom: auto;
    display: inline-block;
    padding: 0 0 0 5px;
}