https://drafts.csswg.org/cssom-view/#the-screen-interface
The Screen Interface
As its name suggests, the Screen interface represents information about the screen of the output device.
[Exposed=Window]
interface Screen {
readonly attribute long availWidth;
readonly attribute long availHeight;
readonly attribute long width;
readonly attribute long height;
readonly attribute unsigned long colorDepth;
readonly attribute unsigned long pixelDepth;
My experience is that "screen" must be lower case in code, so it would help if the text used that. Also it would help immensely to clarify better what is meant by "available width" versus "width"; the whole writeup involving width, height, availWidth, availHeight, innerWidth, outerWidth, innerHeight and outerHeight could use some clarifying examples.