Scroll background image

Hi,
I’ve inserted with a div a background image in a single page.
I insert the code in the page.php <div style="position:fixed;background-image:url('https://link/images/a.gif');background-repeat:no-repeat;background-position:0 0;width:100%;height:100%;z-index:-1000;"></div>
I wouldn’t have a fixed image; if I scroll the page also the image must to scroll.
I’ve tried to modify the code <div style="background-attachment:scroll;background-image:url('https://link/images/a.gif');background-repeat:no-repeat;background-position:0 0;width:100%;height:100%;z-index:-1000;"></div>
In this case the image disappear.
What can I do?