The Eight Digit Hex color is as simple as Six Digit Hex color it contains 8 digits rather than six, it is used to define the color of your elements with the CSS. It has a prefixed hash(#) value before the digits like six-digit hex code.
The difference between 6 and 8 digit hex codes is, that 2 extra characters define the alpha channel as the name suggests in the 8 digit hex color. The last two digits will define that the color will how much transparent or opaque. If the last two digit is 00 then that will be fully transparent and if that is FF then it will be fully opaque.
Note: The first six character represent the RGB color as Six digit hex color code. Last two represent the alpha channel.