使用CSS生成小三角

.sub-menu {
        width: 140px;
        outline: 1px solid #ccc;
        height: 33px;
        position: relative;
      }
      .sub-menu::after {
        content: '';
        position: absolute;
        bottom: 12px;
        right: -5px;
        width: 10px;
        height: 10px;
        border: 1px solid;
        background-color: white;
        border-color: #ccc #ccc transparent transparent;
        transform: rotate(45deg);
      }

效果如下