.block {
      width:400px;
      height:400px;
      position:relative;
 }
.block:before {
      content:"";
      width:1px;
      height:100%;
      display:block;
      left:50%;
      position:absolute;
	    background-image: -webkit-linear-gradient(top, #fff, #000, #fff);
      background-image: -moz-linear-gradient(top, #fff, #000, #fff);
      background-image: -ms-linear-gradient(top, #fff, #000, #fff);
      background-image: -o-linear-gradient(top, #fff, #000, #fff);
      background-image: linear-gradient(top, #fff, #000, #fff);
	}