Template:Mbox/styles.css

td.mbox-image {                /* The left image cell */
	padding: 2px 0 2px 0.9em;  /* 0.9em left, 0px right */
}
td.mbox-imageright {           /* The right image cell */
	padding: 2px 0.9em 2px 0;  /* 0px left, 0.9em right */
}