Disco CSS button

@import url('https://fonts.googleapis.com/css2?family=Syne:wght@400;500;600;700;800&display=swap');

.btn {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  gap: .5em;
  padding: 14px 28px;
  font-family: 'Syne', sans-serif;
  font-size: 16px;
  font-weight: 800;
  line-height: 1.2;
  color: #1e1b4b;
  background: linear-gradient(90deg, #f0abfc 0%, #93c5fd 25%, #fde68a 50%, #f9a8d4 75%, #a5f3fc 100%);
  background-size: 200% 200%;
  border: 1px solid rgba(255, 255, 255, .6999999999999999555910790149937383830547332763671875);
  border-radius: 999px;
  box-shadow: 0 10px 30px -10px rgba(167, 139, 250, .8000000000000000444089209850062616169452667236328125), inset 0 1px 0 0 rgba(255, 255, 255, .8000000000000000444089209850062616169452667236328125);
  position: relative;
  overflow: hidden;
  isolation: isolate;
  cursor: pointer;
  text-decoration: none;
  white-space: nowrap;
  -webkit-tap-highlight-color: transparent;
  transition: transform 200ms cubic-bezier(.2,.8,.2,1), box-shadow 200ms cubic-bezier(.2,.8,.2,1), filter 200ms cubic-bezier(.2,.8,.2,1);
  animation: btn-flow 4s ease-in-out infinite alternate;
}

.btn__icon {
  display: inline-block;
  transition: transform 200ms cubic-bezier(.2,.8,.2,1);
}

.btn::after {
  content: '';
  position: absolute;
  inset: 0;
  background: linear-gradient(110deg, transparent 35%, rgba(255, 255, 255, .45) 50%, transparent 65%);
  transform: translateX(-120%);
  transition: transform .7s ease;
  pointer-events: none;
}

.btn:hover {
  transform: translateY(-3px);
  filter: brightness(1.0500000000000000444089209850062616169452667236328125);
  box-shadow: 0 13px 36px -10px rgba(167, 139, 250, .8000000000000000444089209850062616169452667236328125), inset 0 1px 0 0 rgba(255, 255, 255, .8000000000000000444089209850062616169452667236328125), 0 0 22px 0 rgba(196, 181, 253, .59999999999999997779553950749686919152736663818359375);
}

.btn:hover::after {
  transform: translateX(120%);
}

.btn:hover .btn__icon {
  transform: translateX(3px);
}

.btn:active {
  transform: translateY(1px) scale(0.979999999999999982236431605997495353221893310546875);
  box-shadow: 0 9px 30px -10px rgba(167, 139, 250, .8000000000000000444089209850062616169452667236328125), inset 0 1px 0 0 rgba(255, 255, 255, .8000000000000000444089209850062616169452667236328125);
  transition-duration: 100ms;
}

.btn:focus-visible {
  outline: 3px solid #f0abfc;
  outline-offset: 3px;
}

@keyframes btn-flow {
  from {
    background-position: 0% 50%;
  }
  to {
    background-position: 100% 50%;
  }
}

@media (prefers-reduced-motion: reduce) {
  .btn,
  .btn::after,
  .btn__icon {
    transition: none;
    animation: none;
  }
}

<button class="btn" type="button">
  Dance
  <span class="btn__icon" aria-hidden="true">★</span>
</button>