纯css :after 菜单后面添加“<”

效果：

 1、

.metismenu .has-arrow:after {
    position: absolute;
    content: "";
    width: .50em;
    height: .50em;
    border-style: solid;
    border-width: 1.2px 0 0 1.2px;
    border-color: initial;
    right: 15px;
    transform: rotate(
-45deg) translateY(-50%);
    transform-origin: top;
    top: 50%;
    transition: all .3s ease-out;
    color: #c6d1f9;
}

2、展开

.metismenu .has-arrow[aria-expanded=true]:after, .metismenu .mm-active>.has-arrow:after {

1.  transform: rotate(
    

   -135deg
   ) translateY(-50%);

}