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

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

.prime-list {
  list-style: none;
  counter-reset: item;
  margin: 0;
  padding: 0;
  display: flex;
  flex-direction: column;
  gap: 8px;
  width: 230px;
}

.prime-list li {
  counter-increment: item;
  position: relative;
  padding-left: 32px;
  min-height: 22px;
  display: flex;
  align-items: center;
  color: #17141a;
  font-size: 12px;
}

.prime-list li::before {
  content: counter(item);
  position: absolute;
  left: 0;
  top: 50%;
  width: 22px;
  height: 22px;
  margin-top: -11px;
  border-radius: 50%;
  background: #0a4fe8;
  color: #fff7e6;
  font-size: 11px;
  font-weight: 700;
  display: flex;
  align-items: center;
  justify-content: center;
  box-shadow: 0 0 0 0 rgba(10, 79, 232, 0);
}

.prime-list li.is-prime::before {
  animation: primePulse 2s ease-out infinite;
}

@keyframes primePulse {
  0%, 100% {
    box-shadow: 0 0 0 0 rgba(10, 79, 232, 0.55);
  }
  50% {
    box-shadow: 0 0 0 7px rgba(10, 79, 232, 0);
  }
}
.shift {
  appearance: none;
  border: none;
  margin-top: 16px;
  padding: 8px 16px;
  border-radius: 12px;
  background: #0a4fe8;
  color: #fff7e6;
  font-size: 12px;
  font-weight: 600;
  cursor: pointer;
  transition: transform 140ms ease-out;
}
.shift:hover {
  transform: translateY(-1px);
}
.shift:active {
  transform: scale(0.96);
}
.shift:focus-visible {
  outline: 2px solid #5b8cf8;
  outline-offset: 2px;
}

@media (max-width: 340px) {
  .prime-list {
    width: 260px;
    display: grid;
    grid-template-columns: repeat(2, 1fr);
    gap: 4px;
  }
  .prime-list li {
    font-size: 10px;
    min-height: 20px;
    padding-left: 24px;
  }
  .prime-list li::before {
    width: 18px;
    height: 18px;
    margin-top: -9px;
    font-size: 10px;
  }
  .shift {
    margin-top: 8px;
    padding: 4px 12px;
  }
}
@media (prefers-reduced-motion: reduce) {
  .prime-list li.is-prime::before {
    animation: none;
    box-shadow: 0 0 0 4px rgba(10, 79, 232, 0.35);
  }
  .shift {
    transition: none;
  }
}