When laying out a document, the browser's rendering engine represents each element as a rectangular box according to the standard CSS basic box model . CSS determines the size, position, and properties (color, background, border size, etc.) of these boxes.

Every box is composed of four parts (or areas), defined by their respective edges: the content edge, padding edge, border edge, and margin edge.

The content area, bounded by the content edge, contains the "real" content of the element, such as text, an image, or a video player. Its dimensions are the content width (or content-box width) and the content height (or content-box height). It often has a background color or background image.

If the box-sizing property is set to content-box (default) and if the element is a block element, the content area's size can be explicitly defined with the width, min-width, max-width, height, min-height, and max-height properties. (Source: MDN)