SO http://bit.ly/1es0pUu

HTML

<!--
For a complete solution, remember to include the following in the head of your document  
  
<meta name="viewport" content="width=device-width, initial-scale=1.0">
 
-->  
  
<div id="wrapper">
        <div id="header">
            <img src="logo.jpg" alt="Smiley face" style="height:15%;width:50%;">
        </div>
        <div id="mainWrap">
            <div id="sidebar">
                Sidebar
            </div>
            <div id="main">
                Lorem ipsum dolor sit amet, consetetur sadipscing elitr, sed;
                Lorem ipsum dolor sit amet, consetetur sadipscing elitr, sed;
                Lorem ipsum dolor sit amet, consetetur sadipscing elitr, sed;
                Lorem ipsum dolor sit amet, consetetur sadipscing elitr, sed;
                Lorem ipsum dolor sit amet, consetetur sadipscing elitr, sed;
                Lorem ipsum dolor sit amet, consetetur sadipscing elitr, sed;
                Lorem ipsum dolor sit amet, consetetur sadipscing elitr, sed;
                Lorem ipsum dolor sit amet, consetetur sadipscing elitr, sed;
                Lorem ipsum dolor sit amet, consetetur sadipscing elitr, sed;
                Lorem ipsum dolor sit amet, consetetur sadipscing elitr, sed;
                Lorem ipsum dolor sit amet, consetetur sadipscing elitr, sed;
                Lorem ipsum dolor sit amet, consetetur sadipscing elitr, sed;Lorem ipsum dolor sit amet, consetetur sadipscing elitr, sed;
                Lorem ipsum dolor sit amet, consetetur sadipscing elitr, sed;
                Lorem ipsum dolor sit amet, consetetur sadipscing elitr, sed;
                Lorem ipsum dolor sit amet, consetetur sadipscing elitr, sed;
                Lorem ipsum dolor sit amet, consetetur sadipscing elitr, sed;
                Lorem ipsum dolor sit amet, consetetur sadipscing elitr, sed;Lorem ipsum dolor sit amet, consetetur sadipscing elitr, sed;
                Lorem ipsum dolor sit amet, consetetur sadipscing elitr, sed;
               ...

CSS

#mainWrap{
font-size:0;
    background-color:#aaa;
}
#header{
color:white;
margin-bottom:4em;
    background-color:#ddd;
}


#sidebar{
font-size:12px;
width:25%;
vertical-align:top;
display:inline-block;
    background-color:pink;
}

#main{
font-size:12px;
width:75%;
display:inline-block;
vertical-align:top;
    background-color:olive;

}

#footer{
    font-size:12px;
    border-style: solid;
    background-color:#ffc;
}

@media screen and (max-width:480px){

    #sidebar {
        display:none;
    }
    
    #main{
        width:100%;
    }
}