Most efficient way of putting an internal radius to a border using Edge Animate.

Hi all..

I am looking for a bit of help in solving this one..

If we were to create a rectangle and make that rectangle transparent, then assign a colour to the border, then make it say... 3px we would see a lovely rectangle with rounded edges.

But... How do i add an internal radius to my border...

If i were coding CSS i would do the following, but i would like to know the Edge way of doing this

many thanks as usual!!

If i were in css:

#container {
    float: left;
    border-radius: 3px;
    background-color: #383838;
    width: 174px;
    height: 174px;
}
#container:before {
    border-radius: 3px;
    border: 2px solid #383838;;
    content: '';
    width: 170px;
    height: 170px;
    position: absolute;