Because you say that all the angles of the child element must match the corners of the parent*.
It would be a pretty short article.
* who provided a positioning different from static.
Marcel_Mayer49 answered on March 12th 20 at 08:01
Just check the properties of positioning and absolute positioning, especially with top/left/right/bottom. If you set the opposite value, then they both primenantis and stretched a block. For example, top 0, bottom-50px will do the top edge of the block at level 0 relative to the "block reference", and climbs down to 50px from the same.