The bottom property sets the position of the bottom edge of the element's content, regardless of the thickness of the borders and padding.
The coordinate reference depends on the position property, it usually takes the value relative or absolute.
With relative positioning of an element, the countdown is from the bottom edge of the element's initial position, and with absolute positioning, it is relative to the bottom edge of the browser window. If the parent element is set to position: relative, then the absolute positioning of child elements determines their position from the bottom edge of the parent.
bottom: auto | length | percentage