CSS positioning: relative positioning, absolute positioning and fixed positioning (relative absolute fixed)

Relative positioning: position:relative;

　Does not break away from the document flow, refers to its own static position through top, bottom, left, right positioning, and can be hierarchically graded through z-index.

Absolute positioning: position:absolute;

　 Break away from the document flow, position through top, bottom, left, right, and select its nearest parent element for positioning. When the position of the parent element is static, the absolute element will be positioned at the origin of the body coordinates, which can be positioned through the x-index level Grading.

Fixed positioning: position:fixed;

　The object he fixed here is the visual window instead of the body, or the parent element, which can be hierarchically graded through z-index.