You can use pseudoelements. E.g.
div {
width : 200px;
height : 50px;
position: relative;
z-index : 1;
background: #eee;
}
div:before {
content : "";
position: absolute;
left : 0;
bottom : 0;
height : 1px;
width : 50%; /* or 100px */
border-bottom:1px solid magenta;
}
<div>Item 1</div>
<div>Item 2</div>
No need to use extra markup for presentational purpose. :after is also supported from IE8.
edit:
if you need a right-aligned border, just change left: 0
with right: 0
if you need a center-aligned border just simply set left: 50px;