The background-attachment property specifies whether the background image should scroll or be fixed (will not scroll with the rest of the page):
Specify that the background image should be fixed: body
{
background-image: url("img_tree.png");
background-repeat: no-repeat;
background-position: right top;
background-attachment: fixed;
}Specify that the background image should scroll with the rest of the page: body
{
background-image: url("img_tree.png");
background-repeat: no-repeat;
background-position: right top;
background-attachment: scroll;
}Sets whether a background image is fixed or scrolls with the rest of the page