元素浮动的问题

子元素浮动会导致父元素盒子无法被撑开,导致父元素的样式无法显示,以下介绍几种清除浮动的方法

原代码:

<!DOCTYPE html><html><head lang="en">
    <meta charset="UTF-8">
    <title></title>
    <style type="text/css">
        #content{
            border: 1px red solid;
        }
        .fl{
            border: 1px blueviolet solid;
            height: 100px;
            width: 100px;
            float: left;
        }
        .fr{
            border: 1px green solid;
            height: 200px;
            width: 200px;
            float: right;
        }
    </style></head><body><p id="content">
    <p class="fl">内容一</p>
    <p class="fr">内容二</p></p></body></html>

显示如下:

1、设置父元素高度:

height: 500px; /*设置父元素高度*/


<!DOCTYPE html><html><head lang="en">
    <meta charset="UTF-8">
    <title></title>
    <style type="text/css">
        #content{
            border: 1px red solid;
            height: 500px; /*设置父元素高度*/
        }
        .fl{
            border: 1px blueviolet solid;
            height: 100px;
            width: 100px;
            float: left;
        }
        .fr{
            border: 1px green solid;
            height: 200px;
            width: 200px;
            float: right;
        }
    </style></head><body><p id="content">
    <p class="fl">内容一</p>
    <p class="fr">内容二</p></p></body></html>

2、父元素绝对定位:position:absolute;


<!DOCTYPE html><html><head lang="en">
    <meta charset="UTF-8">
    <title></title>
    <style type="text/css">
        #content{
            border: 1px red solid;
            position: absolute; /*父元素绝对定位*/        }
        .fl{
            border: 1px blueviolet solid;
            height: 100px;
            width: 100px;
            float: left;
        }
        .fr{
            border: 1px green solid;
            height: 200px;
            width: 200px;
            float: right;
        }
    </style></head><body><p id="content">
    <p class="fl">内容一</p>
    <p class="fr">内容二</p></p></body></html>

3、父元素设置overflow:hidden


<!DOCTYPE html><html><head lang="en">
    <meta charset="UTF-8">
    <title></title>
    <style type="text/css">
        #content{
            border: 1px red solid;
            overflow: hidden; 
        }
        .fl{
            border: 1px blueviolet solid;
            height: 100px;
            width: 100px;
            float: left;
        }
        .fr{
            border: 1px green solid;
            height: 200px;
            width: 200px;
            float: right;
        }
    </style></head><body><p id="content">
    <p class="fl">内容一</p>
    <p class="fr">内容二</p></p></body></html>

4、父元素设置浮动:float:left/right


<!DOCTYPE html><html><head lang="en">
    <meta charset="UTF-8">
    <title></title>
    <style type="text/css">
        #content{
            border: 1px red solid;
            float: left; 
        }
        .fl{
            border: 1px blueviolet solid;
            height: 100px;
            width: 100px;
            float: left;
        }
        .fr{
            border: 1px green solid;
            height: 200px;
            width: 200px;
            float: right;
        }
    </style></head><body><p id="content">
    <p class="fl">内容一</p>
    <p class="fr">内容二</p></p></body></html>

5、在子元素最后添加一个空盒子,并设置样式为clear:both;


<!DOCTYPE html><html><head lang="en">
    <meta charset="UTF-8">
    <title></title>
    <style type="text/css">
        #content{
            border: 1px red solid;
        }
        .fl{
            border: 1px blueviolet solid;
            height: 100px;
            width: 100px;
            float: left;
        }
        .fr{
            border: 1px green solid;
            height: 200px;
            width: 200px;
            float: right;
        }
       .clear{
            clear: both;
        } 
    </style></head><body><p id="content">
    <p class="fl">内容一</p>
    <p class="fr">内容二</p>
    <p class="clear"></p></p></body></html>

6、在父元素样式上添加一个伪类,相当于在子元素最后添加一个空盒子,原理与5类似


<!DOCTYPE html><html><head lang="en">
    <meta charset="UTF-8">
    <title></title>
    <style type="text/css">
        #content{
            border: 1px red solid;
        }
        .fl{
            border: 1px blueviolet solid;
            height: 100px;
            width: 100px;
            float: left;
        }
        .fr{
            border: 1px green solid;
            height: 200px;
            width: 200px;
            float: right;
        }
        #content:after{
            content: &#39;&#39;;
            display: block;
            /!*height: 0;*!/
            clear: both;
        }
    </style></head><body><p id="content">
    <p class="fl">内容一</p>
    <p class="fr">内容二</p></p></body></html>

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