White border around image within black border

Anyone know how I can add a thin (1px) white border immediately around an image, that sits within a larger, thicker black border?

If you see here:

https://www.followtheboat.com/2009/08/01/flaming-lipsi/

…you can see the thick black border, but I want to include the white border around the image. This is the code I am using, what should I add to it?

.wp-caption.aligncenter  {
	background-color: #000000;
	font-family: Arial, Helvetica, sans-serif;
	font-size: 12px;
	font-weight: normal;
	color: #FFFFFF;
	display: block;
	margin-left: auto;
	margin-right: auto;
	margin-bottom: 10px;
	margin-top: 10px;
	border: 20px solid #000000;
}

Any help gratefully received.