Woot I got it :)
#page1 {
background-color: #003366;
color: #FFFFFF;
display: inline-block;
}
#page2 {
background-color: #F6BC0C;
color: #000000;
float:left;
}
So with it changing the size I figured it had to be something with the "block type" so I threw the inline-block on them and it worked.. but incorrectly because you have page 2 hidden. So I threw a float on there and it worked.. I can't really explain the logic behind it but this would definitely be a good interview "riddle" lol :P
Here it is working :) http://jsfiddle.net/lookitstony/EdsP4/