it's because you have hr.fancy-line:before
and after positioned absolute which takes it out of the flow of your document. You can make you .container {position:relative;}
which is a possible fix.
This is located in design3.css line 104
hr.fancy-line:before, hr.fancy-line:after {
content: '';
position: absolute;
width: 100%;
It could also be on line 124 of design3.css
body, hr.fancy-line:after {
background: #F4F4F4;
}