css3シャドウの詳しい説明

<style>
   .effect{
       position: relative;
       width: 800px;
       height: 200px;
       background-color: #fff;
       box-shadow: 0px 1px 4px rgba(0,0,0,0.3)
       ,0px 0px 40px rgba(0,0,0,0.1) inset;  //水平和垂直阴影的值都设置为0，阴影会从中间发散至四周。
   }
    .effect:after,.effect:before{
        position: absolute;
        content: &#39;&#39;;
        background: #fff;
        top:50%;
        bottom:0;
        left: 10px;
        right: 10px;
        box-shadow: 0px 0px 20px rgba(0,0,0,0.3);
        z-index: -999;
        border-radius: 100px/10px;
   }</style><div class="effect"></div>