:root {
  --green-dark: #1b4d2e;
  --green-mid: #2e7d32;
  --green-light: #4caf50;
  --cream: #f4f9f4;
  color-scheme: light;
}

* {
  box-sizing: border-box;
}

body {
  margin: 0;
  min-height: 100vh;
  font-family: "Segoe UI", "Noto Sans", "Noto Sans SC", "Noto Sans CJK", Roboto, Arial, sans-serif;
  background: linear-gradient(160deg, var(--green-dark), var(--green-mid));
  color: var(--cream);
}

.hidden {
  display: none !important;
}

/* ---------- Overlay ---------- */

.overlay {
  position: fixed;
  inset: 0;
  background: rgba(10, 30, 15, 0.92);
  display: flex;
  align-items: center;
  justify-content: center;
  z-index: 1000;
  padding: 1.5rem;
}

.overlay-card {
  background: var(--cream);
  color: #14351f;
  border-radius: 16px;
  padding: 2rem;
  max-width: 640px;
  width: 100%;
  box-shadow: 0 20px 60px rgba(0, 0, 0, 0.4);
  text-align: center;
}

.overlay-title {
  margin: 0 0 1.5rem;
  font-size: 1.4rem;
}

.lang-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(150px, 1fr));
  gap: 0.75rem;
}

.lang-btn {
  background: var(--green-mid);
  color: #fff;
  border: none;
  border-radius: 10px;
  padding: 0.85rem 0.5rem;
  font-size: 1rem;
  cursor: pointer;
  transition: background 0.15s ease, transform 0.15s ease;
}

.lang-btn:hover,
.lang-btn:focus-visible {
  background: var(--green-light);
  transform: translateY(-2px);
}

/* ---------- Main content ---------- */

main {
  display: flex;
  flex-direction: column;
  align-items: center;
  min-height: 100vh;
  padding: 2rem 1rem;
}

.content-wrap {
  max-width: 720px;
  width: 100%;
  text-align: center;
}

h1 {
  font-size: clamp(1.8rem, 4vw, 2.8rem);
  margin: 0 0 1.25rem;
  line-height: 1.25;
}

.subtitle {
  font-size: clamp(1rem, 2vw, 1.25rem);
  margin: 0 0 2rem;
  opacity: 0.95;
}

.countdown {
  display: flex;
  justify-content: center;
  gap: 1rem;
  flex-wrap: wrap;
  margin-bottom: 2rem;
}

.countdown-unit {
  background: rgba(255, 255, 255, 0.12);
  border-radius: 12px;
  padding: 1rem 1.25rem;
  min-width: 84px;
}

.countdown-value {
  display: block;
  font-size: clamp(1.6rem, 4vw, 2.4rem);
  font-weight: 700;
  font-variant-numeric: tabular-nums;
}

.countdown-label {
  display: block;
  font-size: 0.8rem;
  text-transform: uppercase;
  letter-spacing: 0.05em;
  opacity: 0.85;
  margin-top: 0.25rem;
}

.comeback-text {
  font-size: clamp(0.95rem, 2vw, 1.1rem);
  opacity: 0.95;
  margin-bottom: 2rem;
}

.change-lang-btn {
  background: transparent;
  border: 1px solid rgba(255, 255, 255, 0.6);
  color: var(--cream);
  padding: 0.6rem 1.4rem;
  border-radius: 999px;
  cursor: pointer;
  font-size: 0.95rem;
  transition: background 0.15s ease;
}

.change-lang-btn:hover,
.change-lang-btn:focus-visible {
  background: rgba(255, 255, 255, 0.15);
}

/* ---------- Tutorial videos ---------- */

.video-section {
  width: 100%;
  max-width: 720px;
  margin-top: 2.5rem;
  text-align: center;
}

.video-section-title {
  font-size: clamp(1.1rem, 2.5vw, 1.5rem);
  margin: 0 0 1.25rem;
}

.video-tab-buttons {
  display: flex;
  gap: 0.5rem;
}

.video-tab-btn {
  flex: 1;
  background: rgba(255, 255, 255, 0.1);
  border: 1px solid rgba(255, 255, 255, 0.3);
  border-bottom: none;
  color: var(--cream);
  padding: 0.75rem 1rem;
  border-radius: 10px 10px 0 0;
  cursor: pointer;
  font-size: 1rem;
  font-weight: 600;
  opacity: 0.8;
  transition: background 0.15s ease, opacity 0.15s ease;
}

.video-tab-btn:hover,
.video-tab-btn:focus-visible {
  background: rgba(255, 255, 255, 0.18);
  opacity: 1;
}

.video-tab-btn.active {
  background: var(--green-light);
  border-color: var(--green-light);
  opacity: 1;
}

.video-tab-btn.active:hover {
  background: var(--green-light);
}

.video-panels {
  background: rgba(0, 0, 0, 0.18);
  border: 1px solid rgba(255, 255, 255, 0.3);
  border-radius: 0 10px 10px 10px;
  padding: 0.75rem;
}

.tutorial-video {
  display: block;
  width: 100%;
  border-radius: 8px;
  background: #000;
}