Mark-up:
<div id="a">A</div>
<div id="b">B</div>
Styling:
#a {
float: left;
width: 30px;
height: 30px;
color: white;
background-color: red;
border: 1px solid black;
text-align: center;
}
#b {
margin-left: 25px;
width: 30px;
height: 40px;
color: white;
background-color: green;
border: 1px solid black;
text-align: center;
}
View the live code example here: http://jsfiddle.net/mxtdg/;
If you want B to be above A instead of below, you can adjust the positioning in your CSS rules.