How to set height of a div element to same as another div

I have two div elements same as the image bellow.

enter image description here

Div 1 : It show contents from server, so can not know the height Div 2 : It’s height should be same as the height of div 1.

I have no experience in HTML (CSS), so I dont know how to do this. Please help me in this case.

Thank a lot.

Answer

HTML

 <div class="container">  
     <div class="Div1">Lorem ipsum dolor sit amet, consectetur adipiscing elit.   
     Etiam congue, tortor in mattis mattis, arcu erat pharetra orci, at vestibulum lorem ante a felis.   
     </div>  
 </div>  

CSS

.Div1, .Div2 {  
    float: none;  
    padding: 20px;  
    vertical-align: top;  
}  
.container {  
    display: table;  
}  
.Div1 {  
    width: 400px;  
    background-color: LightSlateGrey;  
    display: table-cell;  
}  
.Div2 {  
    width: 200px;  
    display: table-cell;  
    background-color: tan;  
}  

Check out this : Fiddle

Both the divs will take same height irrespective of its content length.