You can look at outline with offset but this needs some padding to exists on your div. Or you can absolutely position a border div inside, something like
<div id='parentDiv' style='position:relative'>
<div id='parentDivsContent'></div>
<div id='fakeBordersDiv'
style='position: absolute;width: 100%;
height: 100%;
z-index: 2;
border: 2px solid;
border-radius: 2px;'/>
</div>
You might need to fiddle with margins on the fake borders div to fit it as you like.