This element is 400 pixels wide. If we didn't set the width explicitly, the element would extend to the width of the page, as the body tag is its containing element. On each side of the box, the padding is 20 pixels and the border is 6 pixels, so now the total width of the element is 452 pixels. With the addition of 30 pixels of margins each side the element, the total width claimed by this element is 512 pixels.