html, body {
  margin: 0;
  overflow: hidden;
}

.stage {
  box-sizing: border-box;
  min-height: 100vh;
  display: grid;
  place-items: center;
  margin: 0;
  background: #17141a;
  font-family: -apple-system, "Segoe UI", "Noto Sans KR", sans-serif;
  padding: clamp(8px, 4vw, 24px);
}

.link {
  position: relative;
  display: inline-block;
  padding: 8px 4px;
  color: #fff7e6;
  text-decoration: none;
  font-weight: 700;
  font-size: clamp(18px, 5vw, 26px);
  line-height: 1.2;
}
.link::after {
  content: "";
  position: absolute;
  left: 0;
  right: 0;
  bottom: 0;
  height: 3px;
  background: linear-gradient(90deg, #2f6df6, #ffd23f, #2f6df6);
  background-size: 200% 100%;
  background-position: 0% 0;
  transform: scaleX(0);
  transform-origin: left center;
  transition: transform 220ms ease-out;
}
.link:hover::after, .link:focus-visible::after {
  transform: scaleX(1);
  animation: color-flow 1.4s linear infinite;
}
.link.is-demo::after {
  animation: color-slide-loop 2s ease-out infinite;
}

@keyframes color-flow {
  0% {
    background-position: 0% 0;
  }
  100% {
    background-position: 100% 0;
  }
}
@keyframes color-slide-loop {
  0% {
    transform: scaleX(0);
    background-position: 0% 0;
  }
  15% {
    transform: scaleX(1);
    background-position: 0% 0;
  }
  85% {
    transform: scaleX(1);
    background-position: 100% 0;
  }
  100% {
    transform: scaleX(0);
    background-position: 100% 0;
  }
}
@media (prefers-reduced-motion: reduce) {
  .link::after, .link.is-demo::after {
    transition: none;
    animation: none;
  }
  .link:hover::after, .link:focus-visible::after {
    transform: scaleX(1);
  }
}