<script type="text/javascript" src="http://yandex.st/jquery/1.4.4/jquery.min.js"></script>
<div class="block"></div>
<style type="text/css">
.block{
position: absolute;
margin-top:23px;
background-color: #EFEEEE;
box-shadow: -1px 0 2px 0 rgba(0, 0, 0, 0.5);
-moz-box-shadow: -1px 0 2px 0 rgba(0, 0, 0, 0.5);
-webkit-box-shadow: -1px 0 2px 0 rgba(0, 0, 0, 0.5);
-khtml-box-shadow: -1px 0 2px 0 rgba(0, 0, 0, 0.5);
display: inline-block;
min-width: 200px;
height: 150px;
border-radius: 10px;
padding: 5px 20px;
}
.block:after {
content: '';
position: absolute;
width: 0;
height: 0;
border: 15px solid;
color: transparent;
border-left-color: #EFEEEE;
left: 100%;
top: 50%;
margin-top: -15px;
}
</style>
<script type="text/javascript">
$("body").append('<style class="append">.block:after{top: 15%;}</style>');
setTimeout(function(){$("style.append").remove()},2000)
</script>