Animated Gradient Border

@property --angle {
  syntax: '<angle>';
  initial-value: 0deg;
  inherits: false;
}

.animated-border {
  background: 
    linear-gradient(#131313, #131313) padding-box,
    conic-gradient(from var(--angle), #ff0055, #0044ff, #ff0055) border-box;
  border: 4px solid transparent;
  border-radius: 12px;
  animation: rotate-gradient 3s linear infinite;
}

@keyframes rotate-gradient {
  to {
    --angle: 360deg;
  }
}