CSS Layout Style
CSS Float Style
CSS z-index Property - How does z-index layer really work?
CSS layer refer to applying z-index property to element that overlap to another element.
CSS z-index property set a overlap value and base on overlap value to element positioning set from each other.
CSS z-index property always work with absolute as well as relative positioning value.
CSS z-index possible value 0, positive (1 to 9999) and negative (-1 to -9999) value to set an element.