Find the style for the body
Code:
body{
background-color:#434142;
position:absolute;
width:100%;
height:100%;
min-width:640px;
min-height:480px;
}
and erase the line height:100%
Basically that line sets the hight of the body to 100% of the hight of the screen (since the body is the child of the screen ). Without it the body will stretch according to how much you'll stuff in there. The reason it was there in the first place was because I didn't have enough content, so the bottom corners would've been in the middle of the screen. Hope that makes sense to you.
Keep on coding. 
P.S.
Eventually you should move your styles to the separate file/files so if you have different pages with the same styles you won't have to type them in over and over.
P.S.S.
Try changing min-height to min-height:100% that should set it to the height of the screen or more. I think that should work.
Edit:
In case you don't know how to put styles into separate file:
take everything inside the <style> </style> tags and post it into the new file named "style_main.css"(or whatever you choose to call it). Replace the <style> tags with:
HTML Code:
<link rel="stylesheet" type="text/css" href="design/style_main.css"/>
were "design/style_main.css" is the directory/filename of your stylesheet. This way when you change something you changing it in one place, instead of going to every page.