@media all and (orientation:portrait) {
    @-ms-viewport {
        width:320px;
        user-zoom: fixed;
        max-zoom: 1;
        min-zoom: 1;
    }
}

@media all and (orientation:landscape) {
    @-ms-viewport {
        width:480px;
        user-zoom: fixed;
        max-zoom: 1;
        min-zoom: 1;
    }
}