Featured Page border with gradient – problem

Hello all,

.round-div {
border: 104px solid;

-moz-border-image: -moz-linear-gradient(top, #3acfd5 0%, #3a4ed5 100%);
border-image-slice: 1;
border-radius: 8px;
-moz-border-radius: 8px;
}
I tried to give the border of the featured pages pictures a gradient color.It works fine but after doing this, the “inner” picture is rectangle and not round anymore.
Then i tried to add border-radius …- but it didn’t work.

If i use a normal color for the border – the “inner” picture is round.
Any ideas ?
best ahmed