1.consists of margin border and padding.
2.default width property: is designated to the content box
3.border box property:is designated to the entire box(including padding and border)
4.box-sizing will not be inherited
5.horizontal margin is cumulative (A on the left and B on the right)
6.Vertical margin won't add up, the larger margin wins (2 margins collapsed)
this is because the content of the box is restrained in a very tiny place
overflow parameter (by default is set to visible)