浏览器顶部阴影

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body:before {
          content: "";
          position: fixed;
          top: -10px;
          left: 0;
          width: 100%;
          height: 10px;
          box-shadow: 0px 0px 10px rgba(0,0,0,.8);
          z-index: 100;
}

转自：http://css-tricks.com/snippets/css/top-shadow/