centreing image in Feed

bachamp

Hi, how do you centre an image in a feed content box.

I have been able to add a border around it using this:

.sm-page-widget-feed .sm-feed-item .sm-feed-item-description img {
  border: 5px solid #000;
}

But adding

margin-left: auto;
margin-right: auto;

does nothing.

Any help?