网页进度条一种简单的实现方法

clip：rect(top,right,bottom,left
)

<style>        
.box {            
     width: 200px;           
     height: 20px;            
     background:#ccc;            
     border-radius:10px;           
     position:relative       
      }       
.clip {            
    position: absolute;            
    width: 100%;
   height: 100%;            
   clip: rect(0px,100px,20px,0px);            
   background: red;            
   border-radius:10px;        
   }    
   </style>
<p class=&#39;box&#39;>
    <span class=&#39;clip&#39;></span>
</p>