Non-absolute location usage of absolute absolute positioning

Summarize:

position for the absolute element if left is not set, the top equivalent and left:0;top:0, the effect is not the same. For example, there is a absolute attribute element in a div, which does not have a left or top value, it will remain in the div silently like a normal inline-block attribute element, but once the left:0;top:0 is set; This absolute element immediately becomes detached from the DOM tree, independent of the document flow, with the result relative to the nearest relative attribute's ancestor tag location (if not, the body is positioned).

Non-absolute location usage of absolute absolute positioning