/*html*/ <aside class="ad-area"> <a href="" class="thumb-bd"> <img src="./assets/images/ad2.jpg" alt=""> </a> </aside> /*css*/ .thumb-bd{ display: block; position: relative; } .thumb-bd::before{ position: absolute; top: 0; left: 0; right: 0; bottom: 0; border: 1px solid #000; opacity: 0.1; content: ''; }