The CSS box model is essentially a box that wraps around every HTML element. It consists of: Content - The content of the box, where text and images appear Padding - Clears an area around the content. The padding is transparent Border - A border that goes around the padding and content Margin - Clears an area outside the border. The margin is transparent When you set the width and height properties of an element with CSS, you just set the width and height of the content area. To calculate the full size of an element, you must also add padding, borders and margins. Total element width = width + left padding + right padding + left border + right border + left margin + right margin