如何在滑块缩略图活动浏览器之后添加元素？

Question

我正在尝试在将CSS代码作为伪元素的智能滑块缩略图活动浏览器之后添加图像，但是不起作用

div#n2-ss-2 .nextend-thumbnail-default .nextend-thumbnail-scroller > div.n2-active {
 cursor: default;
 border: 3px solid #b3b3b3;
}


div#n2-ss-2 .nextend-thumbnail-default .nextend-thumbnail-scroller > div.n2-active::after {
 cursor: default;
 position: absolute;
 bottom: -13px;
 left: calc(50% - 20px);
 height: 0;
 width: 0;
 border-color: #b3b3b3 transparent transparent;
 border-style: solid;
 border-width: 16px 18px 0;
 content: url('https://.../wp-content/uploads/2018/09/drop-down-arrow_icon-icons.com_72774.svg');
 display: inline-block;
 z-index: 0;
}