in 'All Style Options' part of the 'Style Manager', find near the bottom of the page 'Additional CSS Definitions' and add the following in the second box
.postbitinfo {
background-color: #E6ECF4;
border-top: 1px solid #4775A7;
border-right: 2px solid #4775A7;
border-left: 1px solid #4775A7;
border-bottom: 2px solid #4775A7;
padding-top: 3px;
padding-right: 0px;
padding-left: 3px;
padding-bottom: 3px;
margin-bottom: 3px;
}
change #E6ECF4 to the background colour you would like and change all 4 instances of #4775A7 to the border color you would like... the colors there are the same (or as close as i could get) to the example you posted
scroll right to the bottom and hit save
then in your 'postbit_legacy' template
find
<div>$vbphrase[join_date]: $post[joindate]</div></if>
change to
<div class="postbitinfo">$vbphrase[join_date]: $post[joindate]</div></if>
also below this code you will see simelar code for the location, age, posts and reputation.... where the div tag starts <div> replace these with <div class="postbitinfo">