Floatinggroup Side bar_website is set to float to both so that the sidebar is anchored to both the top and bottom of the page and allows for scrolling within the floating group. When a floating group is set to both, the floating group height needs to be the same height as the page height (i.e., the bottom of the floating group is aligned with the bottom of the page). If not, then the floating group will "disappear" when you preview the page.