RGBA color expressed using numbers.
background-color: rgba(255, 0, 0, 0.1);
RGBA color expressed using percentages.
background-color: rgba(0%, 100%, 0%, 0.1);
HSL color.
background-color: hsl(240, 100%, 90%);
HSLA color.
background-color: hsla(240, 100%, 90%, 0.25);