opacity: 1
opacity: 0.5
opacity: 0.25
opacity: 0
background-color: rgba(255, 0, 0, 1)
background-color: rgba(255, 0, 0, 0.5)
background-color: rgba(255, 0, 0, 0.25)
background-color: rgba(255, 0, 0, 0)