Use opacity() CSS function that applies transparency to the samples in the input element. There is an alternative Opacity utility you can use instead.
backdrop-opacity-0backdrop-opacity-5backdrop-opacity-10backdrop-opacity-20backdrop-opacity-25backdrop-opacity-30backdrop-opacity-40backdrop-opacity-50backdrop-opacity-60backdrop-opacity-70backdrop-opacity-75backdrop-opacity-80backdrop-opacity-90backdrop-opacity-95backdrop-opacity-100