:root {
  --bg-top: #f2f7ff;
  --bg-bottom: #d7ebff;
  --accent: #2563eb;
  --accent-dark: #1d4ed8;
  --accent-soft: #dbeafe;
  --text-dark: #0f172a;
  --text-muted: #475569;
  --flashcard-border: rgba(37, 99, 235, 0.2);
  --card-bg: rgba(255, 255, 255, 0.76);
  --shadow: 0 24px 48px rgba(37, 99, 235, 0.12);
}

* {
  box-sizing: border-box;
}

html, body {
  margin: 0;
  padding: 0;
  font-family: "Poppins", "Segoe UI", system-ui, -apple-system, BlinkMacSystemFont, sans-serif;
  color: var(--text-dark);
  line-height: 1.5;
  background: linear-gradient(180deg, var(--bg-top) 0%, #e6f1ff 40%, var(--bg-bottom) 100%);
  min-height: 100dvh;
}

body::before {
  content: "";
  position: fixed;
  inset: 0;
  background: radial-gradient(1200px 800px at 70% -200px, rgba(59,130,246,0.18), transparent),
              radial-gradient(800px 600px at -5% 20%, rgba(56,189,248,0.18), transparent);
  pointer-events: none;
  z-index: -1;
}

.hidden {
  display: none !important;
}

.app {
  width: min(1080px, 95%);
  margin: clamp(16px, 4vw, 48px) auto;
  display: flex;
  flex-direction: column;
  gap: clamp(16px, 4vw, 32px);
}

.card,
.quiz,
.result,
.modal-card,
.gallery,
.hero,
.flashcards,
.mode-picker {
  background: var(--card-bg);
  backdrop-filter: blur(14px);
  -webkit-backdrop-filter: blur(14px);
  border-radius: 24px;
  border: 1px solid rgba(148, 163, 184, 0.18);
  box-shadow: var(--shadow);
}

.hero {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(260px, 1fr));
  align-items: center;
  padding: clamp(24px, 6vw, 40px);
  overflow: hidden;
}

.hero-text h1 {
  margin: 0;
  font-size: clamp(28px, 6vw, 42px);
}

.hero-kicker {
  text-transform: uppercase;
  letter-spacing: 0.24em;
  font-size: 12px;
  font-weight: 600;
  color: var(--accent);
  margin: 0 0 6px;
}

.hero-subtitle {
  margin: 12px 0 0;
  color: var(--text-muted);
  max-width: 30ch;
}

.hero-illustration {
  position: relative;
  min-height: 180px;
}

.sun {
  position: absolute;
  top: 20px;
  right: 30px;
  width: 120px;
  height: 120px;
  border-radius: 50%;
  background: radial-gradient(circle at 30% 30%, #fff8b5, #facc15 70%, #f59e0b 100%);
  box-shadow: 0 0 40px rgba(250, 204, 21, 0.4);
}

.cloud {
  position: absolute;
  background: rgba(255, 255, 255, 0.9);
  border-radius: 999px;
  box-shadow: 0 16px 30px rgba(148, 163, 184, 0.25);
}

.cloud-one {
  width: 160px;
  height: 60px;
  bottom: 50px;
  right: 20px;
}

.cloud-two {
  width: 120px;
  height: 46px;
  bottom: 100px;
  right: 140px;
}

.sparkles {
  position: absolute;
  inset: 20px;
  background: radial-gradient(circle at 20% 20%, rgba(255,255,255,0.9) 0, transparent 45%),
              radial-gradient(circle at 80% 30%, rgba(255,255,255,0.6) 0, transparent 40%),
              radial-gradient(circle at 60% 70%, rgba(255,255,255,0.6) 0, transparent 40%);
  opacity: 0.7;
}

.gallery {
  padding: clamp(20px, 5vw, 30px);
}

.gallery-head {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 12px;
  flex-wrap: wrap;
}

.gallery-title {
  margin: 0;
  font-size: clamp(22px, 5vw, 30px);
}

.subject-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(220px, 1fr));
  gap: 18px;
  margin-top: 22px;
}

.subject-card {
  min-height: 88px;
  font-size: clamp(16px, 3vw, 20px);
  font-weight: 600;
  background: linear-gradient(180deg, rgba(255,255,255,0.95) 0%, rgba(226,238,255,0.85) 100%);
  border: 1px solid rgba(148, 163, 184, 0.24);
  color: var(--text-dark);
  transition: transform 0.16s ease, box-shadow 0.2s ease;
}

.subject-card:hover {
  transform: translateY(-4px);
  box-shadow: 0 18px 30px rgba(59, 130, 246, 0.18);
}

.btn {
  border: 0;
  border-radius: 18px;
  padding: 14px 22px;
  cursor: pointer;
  font-size: 16px;
  transition: transform 0.08s ease, box-shadow 0.2s ease, filter 0.2s ease;
  display: inline-flex;
  align-items: center;
  justify-content: center;
  gap: 8px;
  text-decoration: none;
  font-weight: 600;
  color: inherit;
}

.btn:active {
  transform: translateY(2px);
}

.three-d {
  box-shadow: 0 14px 0 rgba(37, 99, 235, 0.2), 0 20px 36px rgba(37, 99, 235, 0.16);
}

.btn.primary {
  background: linear-gradient(180deg, #3b82f6 0%, #1d4ed8 100%);
  color: #fff;
}

.btn.secondary {
  background: linear-gradient(180deg, #bfdbfe 0%, #93c5fd 100%);
  color: #1e3a8a;
  box-shadow: 0 12px 0 rgba(147, 197, 253, 0.6), 0 20px 34px rgba(59, 130, 246, 0.18);
}

.btn.ghost {
  background: linear-gradient(180deg, rgba(255,255,255,0.95) 0%, rgba(226,238,255,0.75) 100%);
  border: 1px solid rgba(148, 163, 184, 0.3);
  color: var(--accent-dark);
  box-shadow: 0 10px 0 rgba(148, 163, 184, 0.2), 0 18px 30px rgba(148, 163, 184, 0.18);
}

.btn.icon {
  padding: 12px;
  width: 48px;
  min-width: 48px;
}

.btn.icon svg,
.btn.icon-only svg {
  width: 22px;
  height: 22px;
  fill: currentColor;
}

.btn.icon-only {
  border-radius: 50%;
  padding: 12px;
  width: 52px;
  min-width: 52px;
}

.mode-picker {
  padding: clamp(24px, 6vw, 32px);
}

.mode-header {
  display: flex;
  align-items: center;
  gap: 16px;
}

.mode-kicker {
  text-transform: uppercase;
  letter-spacing: 0.24em;
  font-size: 12px;
  color: var(--text-muted);
  margin: 0 0 4px;
}

.mode-title {
  margin: 0;
  font-size: clamp(22px, 5vw, 30px);
}

.mode-subtitle {
  margin: 18px 0;
  color: var(--text-muted);
}

.mode-actions {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(220px, 1fr));
  gap: 16px;
}

.mode-btn {
  flex-direction: column;
  align-items: flex-start;
}

.mode-btn-title {
  font-size: 20px;
}

.mode-btn-sub {
  font-size: 14px;
  opacity: 0.85;
}

.flashcards {
  padding: clamp(24px, 6vw, 32px);
  display: flex;
  flex-direction: column;
  gap: 24px;
}

.flash-header {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 12px;
  flex-wrap: wrap;
}

.flash-progress {
  margin: 0;
  font-size: clamp(22px, 5vw, 30px);
}

.flashcard {
  border: 1px solid var(--flashcard-border);
  border-radius: 20px;
  background: linear-gradient(145deg, rgba(255,255,255,0.95), rgba(226,238,255,0.85));
  padding: clamp(24px, 6vw, 32px);
  display: grid;
  gap: 18px;
  min-height: 220px;
}

.flashcard-front,
.flashcard-back {
  display: flex;
  flex-direction: column;
  gap: 8px;
}

.flashcard-back.hidden {
  display: none;
}

.flash-label {
  margin: 0;
  font-size: 14px;
  letter-spacing: 0.22em;
  text-transform: uppercase;
  color: var(--accent-dark);
}

.flash-text {
  margin: 0;
  font-size: clamp(18px, 4vw, 22px);
  font-weight: 500;
}

.flash-actions {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(180px, 1fr));
  gap: 14px;
}

.quiz {
  padding: clamp(24px, 6vw, 32px);
  display: flex;
  flex-direction: column;
  gap: 18px;
}

.quiz-header {
  display: flex;
  align-items: flex-start;
  justify-content: space-between;
  gap: 16px;
  flex-wrap: wrap;
}

.quiz-meta {
  display: flex;
  align-items: center;
  gap: 12px;
}

.progress,
.score {
  font-weight: 700;
  color: var(--accent-dark);
}

.question {
  font-size: clamp(20px, 4.5vw, 26px);
  margin: 0;
}

.options {
  display: grid;
  gap: 12px;
  grid-template-columns: repeat(auto-fit, minmax(240px, 1fr));
}

.option-btn {
  padding: 14px 16px;
  border: 1px solid rgba(148, 163, 184, 0.26);
  border-radius: 16px;
  background: linear-gradient(180deg, rgba(244, 248, 255, 0.95) 0%, rgba(226, 238, 255, 0.85) 100%);
  text-align: left;
  font-size: 16px;
  transition: border-color 0.2s ease, background 0.2s ease;
  cursor: pointer;
}

.option-btn:hover {
  border-color: rgba(59, 130, 246, 0.4);
  background: rgba(219, 234, 254, 0.9);
}

.option-btn.correct {
  border-color: #16a34a;
  background: linear-gradient(180deg, #22c55e 0%, #16a34a 100%);
  color: #fff;
}

.option-btn.wrong {
  border-color: #dc2626;
  background: linear-gradient(180deg, #ef4444 0%, #dc2626 100%);
  color: #fff;
}

.option-btn.disabled {
  opacity: 0.85;
  pointer-events: none;
}

.quiz-actions {
  display: flex;
  justify-content: flex-end;
}

.result {
  padding: clamp(28px, 7vw, 40px);
  text-align: center;
}

.result h2 {
  margin: 0 0 12px;
  font-size: clamp(26px, 6vw, 34px);
}

.result-actions {
  display: flex;
  gap: 14px;
  justify-content: center;
  flex-wrap: wrap;
}

.modal {
  position: fixed;
  inset: 0;
  display: none;
  align-items: center;
  justify-content: center;
  background: radial-gradient(1200px 600px at 50% 10%, rgba(37, 99, 235, 0.12), transparent), rgba(15, 118, 192, 0.28);
  padding: 16px;
  z-index: 1000;
}

.modal.show {
  display: flex;
}

.modal-card {
  width: min(520px, 100%);
  padding: clamp(22px, 5vw, 32px);
}

.title {
  margin: 0 0 8px;
}

.device-id-label {
  font-weight: 600;
  display: block;
  margin-top: 12px;
}

.device-id-row {
  display: flex;
  align-items: stretch;
  gap: 12px;
  margin-top: 10px;
}

.device-id {
  user-select: all;
  padding: 14px;
  border: 1px dashed rgba(59, 130, 246, 0.4);
  border-radius: 16px;
  background: rgba(219, 234, 254, 0.6);
  font-family: ui-monospace, SFMono-Regular, Menlo, Monaco, Consolas, monospace;
  flex: 1;
  font-size: clamp(13px, 3.4vw, 16px);
  word-break: break-all;
  white-space: pre-wrap;
}

.gate-actions {
  display: flex;
  gap: 10px;
  margin-top: 16px;
  flex-wrap: wrap;
}

.gate-msg {
  margin-top: 12px;
  min-height: 22px;
  color: var(--text-dark);
}

.gate-msg.success {
  color: #047857;
}

.app-footer {
  text-align: center;
  font-weight: 600;
  letter-spacing: 0.18em;
  text-transform: uppercase;
  color: var(--accent-dark);
  padding: 32px 16px 40px;
}

@media (max-width: 860px) {
  .hero {
    grid-template-columns: 1fr;
    text-align: center;
  }

  .hero-subtitle {
    margin-left: auto;
    margin-right: auto;
  }

  .hero-illustration {
    min-height: 140px;
  }

  .subject-grid {
    grid-template-columns: repeat(auto-fit, minmax(180px, 1fr));
  }

  .mode-actions {
    grid-template-columns: 1fr;
  }

  .flashcard {
    min-height: 200px;
  }

  .flash-actions {
    grid-template-columns: 1fr;
  }

  .quiz-header {
    flex-direction: column;
    align-items: flex-start;
  }

  .quiz-actions {
    justify-content: center;
  }
}

@media (max-width: 580px) {
  .app {
    margin-top: 12px;
    margin-bottom: 24px;
  }

  .device-id-row {
    flex-direction: column;
  }

  .btn.icon,
  .btn.icon-only {
    align-self: flex-start;
  }
}