CSS Tutorial 46 : Position z index
Z-INDEX
The z-index property specifies the stack order of an element.
An element with greater stack order is always in front of an element with a lower stack order.
Note: z-index only works on positioned elements (position: absolute, position: relative, position: fixed, or position: sticky) and flex items (elements that are direct children of display:flex elements).
Note: If two positioned elements overlap without a z-index specified, the element positioned last in the HTML code will be shown on top.
