Its possible using pseudo element (after).
I have added to the original code a
position:relativeand some margin.
#content{
width: 100px;
min-height: 100px;
margin: 20px auto;
border-style: ridge;
border-color: #567498;
border-spacing:10px;
position:relative;
background:#000;
}
#content:after {
content: '';
position: absolute;
top: -15px;
left: -15px;
right: -15px;
bottom: -15px;
border: red 2px solid;
}