try this:
<a href="#" title="share this" class="tooltip"><span title="share">share</span></a>
css:
.tooltip{
display: inline;
position: relative;
}
.tooltip:hover:after{
background: #333;
background: rgba(0,0,0,.8);
border-radius: 5px;
bottom: 26px;
color: #fff;
content: attr(title);
left: 20%;
padding: 5px 15px;
position: absolute;
z-index: 98;
width: 100%;
}
.tooltip:hover:before{
border: solid;
border-color: #333 transparent;
border-width: 6px 6px 0 6px;
bottom: 20px;
content: "";
left: 50%;
position: absolute;
z-index: 99;
}
working jsfiddle: demo