JsFiddle

标记

<div class="container">
    <div class="cent"></div>
</div>

(相关)CSS

html,body
{
    height: 100%;
}
body
{
   display: table; 
   margin: 0 auto;
}
 
.container
{  
    height: 100%;
    display: table-cell;   
    vertical-align: middle;    
}
.cent
{
    height: 50px;
    width: 50px;
    background-color: black;      
}