Create an expandable ahref button in width, with 3 background image in css (left, middle and right parts). All this keeping the html very simple.

ahref-expandable-button.css

.cbtn {
    position: relative;
    top: 0px;
    left: 9px; /* same as width of left part (:before) */

    background: url(img/middle.png);
    height: 50px; /* height of the background image */

    color: #000;

    display:table-cell;
    vertical-align:middle;
    text-align:center;
    text-decoration: none;
}

.cbtn:before,
.cbtn:after {
    content: "";
    background: url(img/left.png);
    width: 9px; /* width of the image */
    height: 50px; /* height of the background image */
    position: absolute;
    left: -9px; /* same as width */
    top: 0px;
}

.cbtn:after {
    background: url(img/right.png);
    left: auto;
    right: -9px; /* same as width */
}

.cbtn:active {
    color: #000;
}

.cbtn:hover,
.cbtn:hover:before,
.cbtn:hover:after {
    background-position: 0 -50px;
}

.cbtn:active,
.cbtn:active:before,
.cbtn:active:after {
    background-position: 0 -100px;
}

ahref-expandable-button.html

<a href="#" class="cbtn">Click me!!!</a>