全屏显示

 <style>
        #el:-webkit-full-screen{
            border: red solid 3px;
        }
    </style>
<div> 
      <img id="el" src="./img/mm1.jpg" alt=""> 
     <button id="full">全屏显示</button> 
</div> 
  <script>  
     document.querySelector("#full").onclick= function(){ 
     var el = document.getElementById("el"); 
        el.webkitRequestFullScreen() 
     } 
  </script>