1.Login to your blogger dashboard--> layout- -> Edit HTML

2.Scroll down to where you see </head> tag .

3.Copy below code and paste it just before the </head> tag .

<style type='text/css'>
a.tooltip{
position:relative;
text-decoration: none;
}
a.tooltip span{
display: none;
}
a.tooltip:hover span{
display:block;
position:absolute;
top:20px; left:20px;
padding: 5px;
width:200px;
border:1px solid #fff;
background-color:#000000;
filter:alpha(opacity=60);
opacity:0.6;
color:#fff;
}
</style>

4.Now Save your template.

5.Now when your add a link add it as below.

<a href="YOUR-LINK" class="tooltip">LINK-TEXT<span>YOUR-TOOL-TIP-TEXT</span></a>

Look at the example below.

<a href="http://bloggertipandtrick.blogspot.com/" class="tooltip">Blogger Tips<span>Latest Blogger Tips,Tricks</span></a>

It will look like this:

CSS Tooltip For Bloggers