@property --mask-spread{syntax:"<percentage>";inherits:false;initial-value:-40%}.video-mask{-webkit-mask-image:radial-gradient( circle at bottom right, transparent var(--mask-spread,-40%), black calc(var(--mask-spread,-40%) + 40%));mask-image:radial-gradient( circle at bottom right, transparent var(--mask-spread,-40%), black calc(var(--mask-spread,-40%) + 40%));transition:--mask-spread 5s ease-in}