CSS伪元素before与after

• before 在元素内容的前面插入指定的内容.

• after 在元素内容的前面插入指定的内容.

语法

selector::before{
    /* 样式 */
}
selector::after{
    /* 样式 */
}

示例

1.指定文本前后添加内容

<div class="box">test</div>

.box::before{
    content: 'before';
    margin-right:10px ;
}
.box::after{
    content: 'after';
    margin-left:10px ;
}

2.展示指定元素的指定属性内容

<a class="link1" href="http://www.baidu.com"></a><br>
<a class="link2" href="http://www.baidu.com" id="abc"></a>

.link1::after{
    content: ""attr(href)""
}
.link2::after{
    content: ""attr(id)""
}

3.附加图片icon

<i class="icon"></i>

.icon::after{
    content: url(./p1/MTU4MjExNzE5MjM3Ng==582117192376.png);
    width: 20px;
    height: 20px;
    display: block;
}

4. 实现一个书签标记logo

<div class="mark">
    标<br>记
</div>

.mark{
    width: 30px;
    height: 55px;
    color: #fff;
    border-radius: 3px 3px 0 0;
    background-color: red;
    text-align: center;
    position: relative;
    &::after,&::before{
        position: absolute;
        content: '';
        display: block;
        border: 15px solid transparent;
    }
    &::after{
        right: 0;
        border-right: 15px solid red;
        bottom: -15px;
    }
    &::before{
        left: 0;
        border-left: 15px solid red;
        bottom: -15px;
    }
}

5.文字前后自动加上引号

<div class="code">
    content
</div>

.code{
    margin-top: 20px;
    &::before{
        content: "\"";
        color: red;
    }
    &::after{
        content: "\"";
        color: blue;
    }
    &:hover{
        &::before,&::after{
            background-color: yellowgreen;
        }
    }
}

6.自定义样式实现checkbox

<label for="moreAction">
    <input id="moreAction" type="checkbox">
    <span class="fw-checkbox"></span>
    <span>测试</span>
</label>

#moreAction{
    display: none;
}
.fw-checkbox{
    position: relative;
    display: inline-block;
    box-sizing: border-box;
    width: 15px;
    height: 15px;
    border: 1px solid #000;
    border-radius: 2px;
}

#moreAction[type="checkbox"]:checked{
    +.fw-checkbox{
        background-color: crimson;
    }
    +.fw-checkbox::before{
        position: absolute;
        display: inline-block;
        content: '';
        width: 6px;
        height: 10px;
        border-right: 2px solid #fff;
        border-bottom: 2px solid #fff;
        transform: rotate(45deg);
        left: 3px;
        bottom: 3px;
    }
}

7. 简单实现一个聊天气泡

<div class="bubble">
    <img src="./p1/MTU3OTY5OTUwMDM1Mw==579699500353.png" alt="">
    <div class="chat">66666!!!</div>
</div>

.bubble{
    display: flex;
    align-items: center;
    img{
        width: 40px;
        height: 40px;
        border-radius: 50%;
        margin-right: 20px;
    }
    .chat{
        position: relative;
        background-color: cyan;
        padding: 6px;
        border-radius: 4px;
        box-sizing: border-box;
        &::before{
            content: '';
            position: absolute;
            left: -20px;
            border: 10px solid transparent;
            border-right: 10px solid cyan;
        }
    }
}

8. 相片堆叠

 <div class="img-area">
    <div class="pic">
            <img src="./p1/MTU3OTY5OTUwMDM1Mw==579699500353.png" alt="">
        </div>
</div>

.pic{
    position: relative;
    img{
        width: 100%;
        height: 100%;
    }
}

.pic,
.pic::after,
.pic::before{
    width: 200px;
    height: 150px;
    border: 6px solid #fff;
    box-shadow: 2px 2px 5px #ddd;
}

.pic::after,
.pic::before{
    content: '';
    position: absolute;
    background:#eff4de ;
    border: 6px solid #fff;
}

.pic::after{
    transform: rotate(-2deg);
    z-index: -2;
    left: 0px;
}

.pic::before{
    transform: rotate(-5deg);
    z-index: -1;
    left: 0px;
}

参考

1. 掘金:CSS伪元素:before和:after介绍