@property --mask {
    syntax: "<angle>";
    inherits: true;
    initial-value: 0deg
}

.gradient-border:after {
    animation: mask-rotate var(--animationSpeed) linear infinite;
    animation-delay: var(--animation-delay);
    -webkit-mask-image: linear-gradient(hsla(0, 0%, 100%, 0), hsla(0, 0%, 100%, 0)), linear-gradient(#fff, #fff), conic-gradient(from var(--mask), transparent, #000 30%, transparent 100%);
    mask-image: linear-gradient(#fff0, #fff0), linear-gradient(#fff, #fff), conic-gradient(from var(--mask), transparent, #000 30%, transparent 100%)
}

@keyframes mask-rotate {
    to {
        --mask: 1turn
    }
}