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);
}

.ba {
  width: 100%;
  max-width: 300px;
}

.ba__btn {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 12px;
  width: 100%;
  box-sizing: border-box;
  padding: 12px 16px;
  border: 0;
  border-radius: 12px 12px 0 0;
  background: #fff7e6;
  color: #17141a;
  font-weight: 600;
  font-size: 15px;
  box-shadow: 0 6px 12px rgba(23, 20, 26, 0.32);
  transition: border-radius 300ms ease-out, box-shadow 300ms ease-out;
  cursor: pointer;
}

.ba__mark {
  display: inline-flex;
  transition: transform 300ms ease-out;
}

.ba__panel {
  overflow: hidden;
  max-height: 0;
  border-radius: 0 0 12px 12px;
  background: rgba(255, 247, 230, 0.92);
  transition: max-height 600ms cubic-bezier(0.2, 0.8, 0.2, 1);
}

.ba__list {
  list-style: none;
  margin: 0;
  padding: 12px 16px;
  display: grid;
  gap: 8px;
}

.ba__item {
  color: #17141a;
  font-size: 13px;
  opacity: 0;
  transform: translateY(-6px);
  transition: opacity 220ms ease-out, transform 220ms ease-out;
}

.ba--open .ba__btn {
  border-radius: 12px 12px 0 0;
  box-shadow: 0 14px 24px rgba(23, 20, 26, 0.32);
}
.ba--open .ba__mark {
  transform: rotate(180deg);
}
.ba--open .ba__panel {
  max-height: var(--panel-h, 160px);
}
.ba--open .ba__item {
  opacity: 1;
  transform: translateY(0);
}

@media (max-width: 340px) {
  .ba__btn {
    padding: 8px 12px;
    font-size: 14px;
  }
  .ba__list {
    padding: 8px 12px;
  }
}
@media (prefers-reduced-motion: reduce) {
  .ba__btn, .ba__mark, .ba__panel, .ba__item {
    transition: none;
  }
}