div不会扩展浮动内容的高度

<style>
    .container {
        border: 1px solid #ccc;
        overflow: hidden; /* 清除浮动 */
    }
    .float {
        float: left;
        width: 100px;
        height: 100px;
        background-color: #f00;
        margin-right: 10px;
    }
</style>

<div class="container">
    <div class="float"></div>
    <div class="float"></div>
    <div class="float"></div>
</div>