Shiny Button

<div>
  <button>Shiny Button</button>
</div>

button {
  margin-inline: auto;
  display: block;
  position: relative;
}

@property --gradient-angle {
  syntax: '<angle>';
  initial-value: 90deg;
  inherits: false;
}
button::before {
  content: '';
  position: absolute;
  inset: -2px;

  z-index: -1;
  background: linear-gradient(var(--gradient-angle), purple, orange);
  animation: rotate-gradient 4s cubic-bezier(0.37, 0.71, 0.59, 0.19) infinite;
  border-radius: inherit;
}
@keyframes rotate-gradient {
  to {
    --gradient-angle: 360deg;
  }
}