border-image

значения свойства:

none
url()
number
%
thickness
stretch
repeat
round

css/style.css

* {
margin: 0;
padding: 0;
}
.a{
height: 400px;
width: 800px;
position: absolute;
top: 50%;
left: 50%;
margin-top: -230px;
margin-left: -430px;
border: 30px solid #D6E3BC;
border-image: url(img/border.jpg) 30 stretch;
}

* {
 margin: 0;
 padding: 0;
}

.a{
 height: 400px;
 width: 800px;
 position: absolute;
 top: 50%;
 left: 50%;
 margin-top: -230px;
 margin-left: -430px;
 border: 30px solid #D6E3BC;
 border-image: url(img/border.jpg) 30 stretch;
}

index.html

<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8" />
<title>New Page</title>
<link href="css/style.css" rel="stylesheet" />
</head>
<body>
<div class="a"></div>
</body>
</html>

<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8" />
<title>New Page</title>
<link href="css/style.css" rel="stylesheet" />
</head>
<body>
<div class="a"></div>
</body>
</html>