In this lesson from freeCodeCamp's Applied Visual Design section we look at the rgba() background-color attribute. The background-color property can take an rgba value. RGBA stands for red, green, blue, and alpha. Alpha is the level of opacity. 1 is the highest value that is not transparent. Fully transparent would be 0. Half transparent would be .5. Practice with this is helpful and can add a nice visual effect to your elements.