Overlapping Elements
Usually, HTML pages are considered two-dimensional, because the text, images, and other elements are arranged on the page without overlapping. However, in addition to their horizontal and vertical positions, boxes can be stacked along the z-axis as well i.e. one on top of the other by using the CSS z-index property. This property specifies the stack level of a box whose position value is one of absolute, fixed, or relative.
box {
position: absolute;
top: 20px;
right: 30px;
z-index: 2;
}