Say I have the following HTML:
<head>
<style>
#container {
border: 1px red solid;
}
.floaty {
width: 200px;
float: left;
border: 1px green solid;
}
</style>
</head>
<body>
<div id='container'>
Text inside the container
<div class='floaty'>
Floaty block 1<br/>
Floaty block 1<br/>
Floaty block 1<br/>
</div>
<div class='floaty'>
Floaty block 2<br/>
Floaty block 2<br/>
Floaty block 2<br/>
</div>
<div class='floaty'>
Floaty block 3<br/>
Floaty block 3<br/>
Floaty block 3<br/>
</div>
</div>
</body>
This renders as: 
What’s the proper CSS way to have the container (red-bordered box) completely surround the floaty green-bordered boxes?
overflow: autoto the container or apply a clearfix.Add an
overflow: autoto the container, like this:You can test the effect here, and find a very good description of how it works here.