清除浮动的方式

1. 给父级定义height

.parent {
    background-color: red;
}
.float-left {
    width: 200px;
    height: 200px;
    float: left;
}

<div class="parent">
      <div class="float-left"></div>
</div>

2. 在结尾处添加空div，样式设置为clear: both

.parent {
    background-color: red;
}
.float-left {
    width: 200px;
    height: 200px;
    float: left;
}

<div class="parent">
    <div class="float-left"></div>
    <div style="clear: both"></div>
</div>

3. 父级定义伪类

.parent {
    background-color: red;
}
.float-left {
    width: 200px;
    height: 200px;
    float: left;
}
.clearfloat:after {
    display: block;
    clear: both;
    content: '';
    visibility: hidden;
    height: 0;
    zoom: 1;
}

<div class="parent clearfloat">
    <div class="float-left"></div>
</div>

4. 把父级变成BFC

生成BFC的条件

1. 根元素
2. float的值不为none
3. overflow的值不为visible
4. display的值为inline-block、table-cell、table-caption
5. position的值为absolute或fixed

.parent {
    background-color: red;
    float: left;
}

.parent {
    background-color: red;
    overflow: hidden;
}

.parent {
    background-color: red;
    display: table-cell;
}

.parent {
    background-color: red;
   	position: absolute;
}