We can "float" divs next to each other by putting them in order in a container div. For example, this page is styled as follows:

#container {
width: 700px;
height: 800px;
background-color: #ffcc33;
margin: auto;
border: solid 1px;
}
#zeroth {
width: 400px;
float: left;
background-color: #fffff0;
}
#first {
width: 100px;
float: left;
height: 300px;
background-color: blue;
color: white;
}
#second1 {
width: 200px;
float: left;
height: 300px;
background-color: green;

Just put a few words in here so that we are absolutely sure that this area is independent of the green area.