Inner margin, margin description-----

Before 1.ie6, the width and height properties were both border and padding, except for IE browsers, where other browsers defined the width and Height properties as the distance between the left inner margin and the right padding, while the height represents the distance between the upper and lower inner margin boundaries.

2. When you specify a background for an element, it affects the padding, but does not affect the margin, that is, I set the padding to a value, it is obvious that the background range is larger, but the background will not be affected by the margin.

3.

Inner margin, margin description-----