Question

Given the following

#container {
    border:solid 3px red;
}

#left {
    float: left;
    background-color: lightblue;
    height: 300px;
}

#right {
    float: left;
    background-color: coral;
    height: 300px;
}

<div id='container'>
    <div id='left'>Left content</div>
    <div id='right'>Right content</div>
</div>

(See: http://jsfiddle.net/ericjohannsen/JCPEH/1/)

Why does container apparently not have any area (that is, it has a zero height, plus the border)? I naively expected it to be as tall as the child divs that it contains.

What is the proper way to set this up so that the div containing the two children is as tall as the children?

Answer 1

You need to clear your floats. You can do this via a clearfix class:

.clearfix:before,
.clearfix:after {
    content: " "; 
    display: table; 
}

.clearfix:after {
    clear: both;
}

.clearfix {
    *zoom: 1;
}

#container {
    border:solid 3px red;
}

#left {
    float: left;
    background-color: lightblue;
    height: 300px;
}

#right {
    float: left;
    background-color: coral;
    height: 300px;
}

<div id='container' class="clearfix">
    <div id='left'>Left content</div>
    <div id='right'>Right content</div>
</div>

or a clearing element:

.clear {
  clear:both;
}

#container {
    border:solid 3px red;
}

#left {
    float: left;
    background-color: lightblue;
    height: 300px;
}

#right {
    float: left;
    background-color: coral;
    height: 300px;
}

<div id='container'>
    <div id='left'>Left content</div>
    <div id='right'>Right content</div>
    <div class="clear"><!-- --></div>
</div>

Updated Fiddle:
http://jsfiddle.net/JCPEH/5/