do vertical align

CSS

<div id="main">
  <div id="abc">
    <span>content</span>
  </div>
</div>

body{
  padding: 0;
  margin: 0;
    margin:0px auto;
}
#main{
  position: relative;
  background-color:blue;
  width:500px;
  height:500px;
}
#abc{
  font:Verdana, Geneva, sans-serif;
  font-size:18px;
  text-align:left;
  background-color:#0F0;
  height:50px;
    display: table;
    width: 100%;
}

#abc span {
  vertical-align:middle;
  display: table-cell;
}