<!DOCTYPE html>
<html>
<head>
<title>Title of the document</title>
<style>
a.tooltip {
border-bottom: 1px dashed;
text-decoration: none;
}
a.tooltip:hover {
cursor: help;
position: relative;
}
a.tooltip span {
display: none;
}
a.tooltip:hover span {
border: #666 2px dotted;
padding: 5px 20px 5px 5px;
display: block;
z-index: 100;
background: #e3e3e3;
left: 0px;
margin: 15px;
width: 300px;
position: absolute;
top: 15px;
text-decoration: none;
}
</style>
</head>
<body>
<a href="#" class="tooltip">Mouse over the link
<span>CSS tooltip showing up when your mouse over the link</span>
</a>
</body>