css简单实现带箭头的边框

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css简单实现带箭头的边框

普通边框

<style>
    .border {
        width: 100px;
        height: 50px;
        border: 1px solid red;
    }
</style>
<div class="border"></div>

实现由四个三角形组成的正方形

<style>
    .triangle {
        width: 0;
        height: 0;
        border: 100px solid red;
        border-right-color: green;
        border-left-color: blue;
        border-top-color: black;
    }
</style>
<div class="triangle"></div>

向下三角形

<style>
    .triangle-bottom {
        width: 0;
        height: 0;
        border: 100px solid transparent;
        border-top-color: red;
    }
</style>
<div class="triangle-bottom"></div>

将左右下边颜色设置为透明 transparent，得到向下的箭头

将三角形放入边框中

<style>
    .border-triangle {
        width: 100px;
        height: 50px;
        border: 1px solid red;
        position: relative;
    }

    .border-triangle:before {
        content: "";
        position: absolute;
        width: 0;
        height: 0;
        border: 4px solid transparent;
        border-top-color: red;
        left: 50%;
        margin-left: -4px;
        bottom: -8px;
    }
</style>
<div class="border-triangle"></div>

将三角形设置为绝对定位，利用margin-left和left 定位到元素中间，bottom设置-8px，靠近边框底部居中

带箭头的边框

<style>
    .border-triangle-bottom {
        width: 100px;
        height: 30px;
        border: 1px solid #1d9cd6;
        position: relative;
        border-radius: 4px;
    }

    .border-triangle-bottom:after,
    .border-triangle-bottom:before {
        content: "";
        position: absolute;
        width: 0;
        height: 0;
        border: 4px solid transparent;
        border-top-color: #1d9cd6;
        left: 50%;
        margin-left: -4px;
        bottom: -8px;
    }

    .border-triangle-bottom:after {
        border-top-color: #fff;
        bottom: -7px;
    }
</style>
<div class="border-triangle-bottom"></div>

将边框颜色换成好看的蓝色，将before和after伪元素都设置为绝对定位，定位到边框底部剧中，将after伪元素设置成白色，底部偏移量大于before 1px，遮住三角形底部的颜色。这样一个好看的箭头边框就实现了