透明度を変えてみよう

opacity

opacity: 1

opacity: 0.5

opacity: 0.25

opacity: 0

rgba()

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)