MDN Web Docs CSS Backgrounds
Background position is a background property in CSS used to determine the position of a background element. This property is sometimes quite useful for placing certain elements, especially background images, in specific areas to act as a page marker or design feature of the page.
According to MDN, 'CSS property sets whether a background image's position is fixed within the viewport, or scrolls with its containing block'. Like the previous background property, this one is mostly for looks and giving the page more of a interactive feel to it.
The background size element allows the developer to specify how much space a background takes up. The background can be left it's regular size, stretched, or constrained to fit (or not fit) in a given space. Also, 'Spaces not covered by a background image are filled with the background-color property, and the background color will be visible behind background images that have transparency/translucency.'
The background edge offset value provides a space between the content and its background and the border of the content. Basically, there is white (or whatever color background) space bewteen the content and the content's border.
The background multiple stack order is essentially the order that backgrounds are in when there are multiple backgrounds provided. According to MDN, 'These are layered atop one another with the first background you provide on top and the last background listed in the back. Only the last background can include a background color.'
To summarize, backgrounds are quite a versatile part of the css design process. Backgrounds alone can be used to do a great number of things, including layout, interactivity, and more.