If you drag, shrink, pull, push and widen this page you will notice that the background image not only continuously fills your browser window, but it's also keeping the image in scale. Meaning the image is not a fixed size where someone who has their screen resolution set to 800x600 will miss the majority of the image, where as someone who has their monitor set to 1440x900 is able to see most of it. This site is able to achieve the effect thanks to the "cover" attribute for background-size in CSS3.