不bb,直接上代码

• html

<div class="arrow_box">CSS ARROW</div>

• css

.arrow_box {
    position: relative;
    background: #88b7d5;
    border: 4px solid #c2e1f5;
}
.arrow_box:after, .arrow_box:before {
    bottom: 100%;
    left: 50%;
    border: solid transparent;
    content: " ";
    height: 0;
    width: 0;
    position: absolute;
    pointer-events: none;
}

.arrow_box:after {
    border-color: rgba(136, 183, 213, 0);
    border-bottom-color: #88b7d5;
    border-width: 30px;
    margin-left: -30px;
}
.arrow_box:before {
    border-color: rgba(194, 225, 245, 0);
    border-bottom-color: #c2e1f5;
    border-width: 36px;
    margin-left: -36px;
}

• 效果

  
  
  image.png

• 结语
  仅作为笔记记录.以下网址可以动态设置反向大小
  "CV地址" : http://www.cssarrowplease.com/