CSS z-index property
z-index property specifies the stack order of an element.
When elements are positioned, they can overlap other elements.
z-index property specifies the stack order of an element (which element should be placed in front of, or behind, the others).
An element can have a positive or negative stack order.
z-index: number | auto | inherit | initial;
z-index only works on positioned elements (
position: fixed, or
position: sticky) and flex items (elements that are direct children of
display: flex elements).
If two positioned elements overlap each other without a
z-index specified, the element defined last in the HTML code will be shown on top.