Hello World Example

HTML

<div id='main'>
Lorem ipsum dolor sit amet, consectetur adipiscing elit. Donec mattis tortor a nisl rhoncus, vitae aliquet lectus sodales.
</div>
<div id="footer">Footer Goes Here</div>

CSS

body {
    background-color: gray;
    max-width:800px;
    margin: 0 auto;
    margin-top:0px;
}
#main {
    background-color: white;
   height: calc(100vh - 50px);
}
#footer {
    text-align: center;
    max-width: 800px;
    background-color: white;
    position: fixed;
    bottom: 0px;
    width: 100%;
    margin: 0 auto;
    height:50px;
}