A box in CSS consists of a content area, which is where any text, images, or other HTML elements are displayed. This is optionally surrounded by padding, a border, and a margin, on one or more sides. The box model describes how these elements work together to create a box as displayed by CSS. To learn more about it read Introduction to the CSS Box Model.

The Box Model specification defines a set of keywords that refer to the edges of each part of the box, these are used as keyword values in CSS including as a value for the box-sizing property, to control how the box model calculates its size.

content-box

The edge of the content area of the box.

padding-box

The edge of the padding of the box, if there is no padding on a side then this is the same as content-box.

border-box

The edge of the border of the box, if there is no border on a side then this is the same as padding-box.

margin-box

The edge of the margin of the box, if there is no margin on a side then this is the same as border-box.

stroke-box

In SVG refers to the stroke bounding box, in CSS treated as content-box.

view-box

In SVG refers to the nearest SVG viewport element's origin box, which is a rectangle with the width and height of the initial SVG user coordinate system established by the viewBox attribute for that element. In CSS treated as border-box.

Margins surround the border edge of a box, and provide spacing between boxes.

• margin
• margin-bottom
• margin-left
• margin-right
• margin-top
• margin-trim Experimental

Padding is inserted between the content edge and border edge of a box.

• padding
• padding-bottom
• padding-left
• padding-right
• padding-top

There are other properties that relate to the box model, that are defined elsewhere.

Borders

The border properties specify the thickness of the border, drawing style and color.

Overflow

Controls what happens when there is too much content to fit into a box.

Introduction to the CSS box model

Explains one of the fundamental concept of CSS: the box model. This model defines how CSS lays out elements, including their content, padding, border, and margin areas.

Mastering margin collapsing

Sometimes, two adjacent margins are collapsed into one. This article describes the rules that govern when and why this happens, and how to control it.

Visual formatting model

Explains the visual formatting model.