transparent background color

Background color transparent:
opacity: transparency.
    Value: between 0 and 1. 0: completely transparent; 1: opaque.
    Problem: When the background is transparent, the text on the element will be transparent together.

rgba: transparent. Transparent background only. Format: (number, number, number, opacity value).
    Description: The first three numbers are rgb values, and the last parameter is the value of opacity.
         rgba is written in the backgroud.
    Example: background:rgba(0,0,0,0.5)-->The background color is black and the transparency is 0.5