ID in CLASS

<div id="vsebina">
      <div class="reference"></div>
      <div class="reference"></div>
      <div class="reference"></div>

CSS:
#vsebina .reference {
	height: 150px;
	width: 150px;
	top: 553px;
	left: 433px;
	position: absolute;
	margin-right: 20px;
	border: 2px solid #666;
	float: left;
	-webkit-border-top-left-radius: 10px;
	-webkit-border-bottom-right-radius: 10px;
	-moz-border-radius-topleft: 10px;
	-moz-border-radius-bottomright: 10px;
	border-top-left-radius: 10px;
	border-bottom-right-radius: 10px;
}