Changes
width: 100%;
height: auto;
}
div.borderimg {
#borderimg1 {
border: 10px solid transparent;
padding: 15px;
-webkit-border-image: url(images/borderimagemobile.jpg) 30 round; /* Safari 3.1-5 */
-o-border-image: url(images/borderimagemobile.jpg) 30 round; /* Opera 11-12.1 */
border-image: url(images/borderimagemobile.jpg) 30 round;
}
