position: absolute

The element is removed from the normal document flow, and no space is created for the element in the page layout. The element is positioned relative to its closest positioned ancestor (if any) or to the initial containing block. Its final position is determined by the values of top, right, bottom, and left. This value creates a new stacking context when the value of z-index is not auto. The margins of absolutely positioned boxes do not collapse with other margins.

Example
When ancestor's position is set (position: relative)
top: 1rem;
left: 2.5rem;
When ancestor's position is not set (postion: static, default)
BOX2 should be here when position is set to static.
Second
bottom: 1rem;
left: 2.5rem;