没搞懂的一段css

.left{
    100px;
    height:100px;
    background-color:#eeeeee;
    border:1px solid green;

    float:left;
}
.right{
    100px;
    height:100px;
    background-color:#aaaaaa;
    border:1px solid red;

    float:right;
}
#b{
    100px;
    height:100px;
    background-color:#555555;
    border:1px solid pink;
    //float:left;
    //clear:left;
}
<html>
<head>
<meta charset="utf-8">
<link type="text/css" rel="stylesheet" href="tmp.css">
</head>
<body>

    <div class="left">A</div>
    <div class="left">B</div>
    <div class="right">C</div>
    <div id="b">X</div>

</body>
</html>

View Code

还没有懂。记下来以后再解释吧。