HTML图像位于其他控件之上

I want to have my background image span the entire page. This works as it should, with the exception of it sits on top of any other control/element I may add to the page. What do I alter in order for me to be able to have an image as a background spanning the entire page as well as add text/images on top of it? This is my current syntax:I want to have my background image span the ent