/* Tell the browser to render HTML 5 elements as block */  
header, footer, aside {  
    display: block;  
} 

#content {  
  display: table;  
}  
      
#mainContent {  
  display: table-cell;  
  width: 620px;  
  padding-right: 22px;  
}  
      
aside {  
  display: table-cell;  
  width: 300px;  
}