iframe{
 border:10px solid transparent;
 border-image-source:url(https://i.imgur.com/91tJ1qi.png);
 border-image-slice:10;
 width:500px;
 height:300px;
 display:block;
 margin:auto;
}

.box {
 position: relative;
 margin: 0px;
 display: block;
 width: 600px;
 height: 420px;
 margin-top: 15%;
}