The top property in CSS goes hand in hand with positioning. By default, elements are static positioned in which the top property has no effect whatsoever. But when the positioning of an element is relative, absolute, or fixed, the top value plays a big role.
div {
top: value (px, em, %, pt, etc) || auto || inherit; /* can be negative */
}
The value for top is any of the valid lengths of CSS.
"The Nudge" (Relative Position)