Use CSS hex code colors with alpha values

Adding an Alpha Value to CSS Hex Codes

Using an alpha value to update a color’s transparency will change the hex code format from #RRGGBB to #RRGGBBAA (where alpha is A).

The AA value in #RRGGBBAA can range from the lowest value possible (00) to the highest value possible (FF). Lowering the value will cause the visibility to become fainter and fainter until it becomes transparent. Raising the value will cause the visibility to become more and more opaque.

div {
  background-color: #0080FF80;
}