Background transparent by using Hexadecimal Color

How to make background color as a transparent color with Hexadecimal color.

If you provide 6 hex digits, that means RGB (2 hex digits for each value of red, green and blue). Each 2-digit hex value is one byte, representing values from 0-255.
Ex. #424242
#RRGGBB

If you provide 8 hex digits, it's an ARGB (2 hex digits for each value of alpha, red, green and blue respectively).
First two digit is Alpha value.
Ex. #66424242
#AARRGGBB

100% — FF
95% — F2
90% — E6
85% — D9
80% — CC
75% — BF
70% — B3
65% — A6
60% — 99
55% — 8C
50% — 80
45% — 73
40% — 66
35% — 59
30% — 4D
25% — 40
20% — 33
15% — 26
10% — 1A
5% — 0D
0% — 00