/* ============================================================================
   KANJI FLASHCARD GAME - CLEAN DESIGN
   ========================================================================== */

* {
  box-sizing: border-box;
}

html, body {
  margin: 0;
  padding: 0;
  height: 100%;
  font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, "Helvetica Neue", sans-serif;
  background-color: #f8f9fa;
  color: #1a1a1a;
}

@media (prefers-color-scheme: dark) {
  html, body {
    background-color: #0f1419;
    color: #ffffff;
  }
}

body {
  display: flex;
  justify-content: center;
  align-items: center;
  min-height: 100vh;
  padding: 16px;
}

.container {
  width: 100%;
  max-width: 960px;
}

/* ============================================================================
   SCREENS / PAGES
   ========================================================================== */

.screen {
  opacity: 1;
  visibility: visible;
  transition: opacity 0.3s ease, visibility 0.3s ease;
}

.screen.hidden {
  opacity: 0;
  visibility: hidden;
  position: absolute;
  pointer-events: none;
}

/* ============================================================================
   CHAPTER SELECT SCREEN
   ========================================================================== */

#chapterSelectScreen {
  background: white;
  border-radius: 12px;
  padding: 48px 32px;
  box-shadow: 0 1px 3px rgba(0, 0, 0, 0.12), 0 1px 2px rgba(0, 0, 0, 0.24);
}

@media (prefers-color-scheme: dark) {
  #chapterSelectScreen {
    background: #1a1f2e;
  }
}

#chapterSelectScreen h1 {
  font-size: 32px;
  font-weight: 600;
  margin: 0 0 8px 0;
  letter-spacing: -0.5px;
}

.subtitle {
  font-size: 14px;
  color: #666;
  margin: 0 0 32px 0;
  font-weight: 400;
}

@media (prefers-color-scheme: dark) {
  .subtitle {
    color: #999;
  }
}

.chapter-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(70px, 1fr));
  gap: 12px;
  margin-bottom: 32px;
  max-width: 600px;
}

.chapter-btn {
  padding: 16px;
  border: 1px solid #d0d0d0;
  background: white;
  color: #1a1a1a;
  border-radius: 8px;
  font-size: 16px;
  font-weight: 500;
  cursor: pointer;
  transition: all 0.2s ease;
  min-height: 60px;
  display: flex;
  align-items: center;
  justify-content: center;
}

@media (prefers-color-scheme: dark) {
  .chapter-btn {
    background: #252d3a;
    border-color: #3a4654;
    color: #ffffff;
  }
}

.chapter-btn:hover {
  border-color: #ff9500;
  background: #fff8f0;
  transform: translateY(-2px);
  box-shadow: 0 2px 8px rgba(255, 149, 0, 0.15);
}

@media (prefers-color-scheme: dark) {
  .chapter-btn:hover {
    background: #2a3346;
    border-color: #ff9500;
  }
}

.chapter-btn:active {
  transform: translateY(0);
  box-shadow: none;
}

.stats {
  padding: 16px;
  background: #f5f5f5;
  border-radius: 8px;
  font-size: 14px;
  color: #666;
  text-align: center;
}

@media (prefers-color-scheme: dark) {
  .stats {
    background: #252d3a;
    color: #aaa;
  }
}

/* ============================================================================
   GAME SCREEN
   ========================================================================== */

#gameScreen {
  background: white;
  border-radius: 12px;
  padding: 32px;
  box-shadow: 0 1px 3px rgba(0, 0, 0, 0.12), 0 1px 2px rgba(0, 0, 0, 0.24);
}

@media (prefers-color-scheme: dark) {
  #gameScreen {
    background: #1a1f2e;
  }
}

.header {
  display: flex;
  align-items: center;
  gap: 24px;
  margin-bottom: 32px;
  flex-wrap: wrap;
}

.back-btn {
  padding: 8px 16px;
  background: transparent;
  border: 1px solid #d0d0d0;
  border-radius: 6px;
  cursor: pointer;
  font-size: 14px;
  color: #666;
  font-weight: 500;
  transition: all 0.2s ease;
  white-space: nowrap;
}

@media (prefers-color-scheme: dark) {
  .back-btn {
    border-color: #3a4654;
    color: #bbb;
  }
}

.back-btn:hover {
  background: #f5f5f5;
  border-color: #999;
  color: #1a1a1a;
}

@media (prefers-color-scheme: dark) {
  .back-btn:hover {
    background: #252d3a;
    border-color: #555;
    color: #fff;
  }
}

#chapterTitle {
  font-size: 24px;
  font-weight: 600;
  margin: 0;
  flex: 1;
  min-width: 100px;
}

.progress {
  flex: 1;
  height: 4px;
  background: #e0e0e0;
  border-radius: 2px;
  overflow: hidden;
  min-width: 120px;
}

@media (prefers-color-scheme: dark) {
  .progress {
    background: #3a4654;
  }
}

.progress-bar {
  height: 100%;
  background: #ff9500;
  border-radius: 2px;
  width: 0%;
  transition: width 0.3s ease;
}

/* ============================================================================
   FLASHCARD
   ========================================================================== */

.card-container {
  perspective: 1000px;
  display: flex;
  justify-content: center;
  margin: 48px 0;
  cursor: pointer;
}

.card {
  width: 100%;
  max-width: 400px;
  aspect-ratio: 1;
  transition: transform 0.6s cubic-bezier(0.68, -0.55, 0.265, 1.55);
  transform-style: preserve-3d;
  position: relative;
}

.card.flipped {
  transform: rotateY(180deg);
}

.front,
.back {
  position: absolute;
  width: 100%;
  height: 100%;
  backface-visibility: hidden;
  display: flex;
  flex-direction: column;
  justify-content: center;
  align-items: center;
  border-radius: 12px;
  padding: 24px;
  text-align: center;
}

.front {
  background: white;
  border: 2px solid #e5e7eb;
  box-shadow: 0 4px 12px rgba(0, 0, 0, 0.08);
}

@media (prefers-color-scheme: dark) {
  .front {
    background: #252d3a;
    border-color: #3a4654;
  }
}

.back {
  transform: rotateY(180deg);
  background: #ff9500;
  border: 2px solid #ff9500;
  color: white;
}

.front p,
.back p {
  margin: 8px 0 0 0;
  font-size: 13px;
  opacity: 0.65;
}

.back p {
  opacity: 0.9;
}

#kanjiDisplay {
  font-size: 80px;
  margin: 0;
  font-weight: 600;
  line-height: 1;
}

#yomikataDisplay {
  font-size: 18px;
  margin: 20px 0 8px 0;
  font-weight: 500;
  color: white;
}

#artiDisplay {
  font-size: 16px;
  margin: 0;
  color: white;
}

/* ============================================================================
   CONTROLS
   ========================================================================== */

.controls {
  display: flex;
  justify-content: center;
  align-items: center;
  gap: 12px;
  margin: 32px 0;
  flex-wrap: wrap;
}

.btn-nav {
  padding: 10px 20px;
  background: #ff9500;
  color: white;
  border: none;
  border-radius: 6px;
  cursor: pointer;
  font-size: 14px;
  font-weight: 500;
  transition: all 0.2s ease;
  white-space: nowrap;
}

.btn-nav:hover {
  background: #e68900;
  transform: translateY(-1px);
  box-shadow: 0 2px 8px rgba(255, 149, 0, 0.3);
}

.btn-nav:active {
  transform: translateY(0);
  box-shadow: none;
}

.counter {
  padding: 10px 20px;
  background: #f5f5f5;
  border-radius: 6px;
  font-weight: 500;
  color: #ff9500;
  min-width: 100px;
  text-align: center;
  font-size: 14px;
}

@media (prefers-color-scheme: dark) {
  .counter {
    background: #252d3a;
    color: #ffb84d;
  }
}

.card-info {
  text-align: center;
  color: #999;
  font-size: 12px;
  margin-top: 16px;
}

@media (prefers-color-scheme: dark) {
  .card-info {
    color: #666;
  }
}

/* ============================================================================
   RESPONSIVE
   ========================================================================== */

@media (max-width: 768px) {
  #chapterSelectScreen {
    padding: 32px 20px;
  }

  #chapterSelectScreen h1 {
    font-size: 28px;
  }

  .chapter-grid {
    grid-template-columns: repeat(auto-fit, minmax(65px, 1fr));
    gap: 10px;
  }

  #gameScreen {
    padding: 20px;
  }

  .header {
    gap: 16px;
    margin-bottom: 24px;
  }

  #chapterTitle {
    font-size: 20px;
  }

  .back-btn {
    padding: 6px 12px;
    font-size: 13px;
  }

  .card-container {
    margin: 32px 0;
  }

  #kanjiDisplay {
    font-size: 60px;
  }

  #yomikataDisplay {
    font-size: 16px;
  }

  #artiDisplay {
    font-size: 14px;
  }

  .controls {
    gap: 8px;
    margin: 24px 0;
  }

  .btn-nav {
    padding: 8px 16px;
    font-size: 13px;
  }

  .counter {
    padding: 8px 16px;
    font-size: 13px;
  }
}

@media (max-width: 480px) {
  body {
    padding: 12px;
  }

  #chapterSelectScreen {
    padding: 24px 16px;
  }

  #chapterSelectScreen h1 {
    font-size: 24px;
  }

  .subtitle {
    font-size: 13px;
  }

  .chapter-grid {
    grid-template-columns: repeat(auto-fit, minmax(60px, 1fr));
    gap: 8px;
    margin-bottom: 24px;
  }

  .chapter-btn {
    padding: 12px;
    font-size: 15px;
    min-height: 56px;
  }

  #gameScreen {
    padding: 16px;
  }

  .header {
    gap: 12px;
    margin-bottom: 20px;
  }

  #chapterTitle {
    font-size: 18px;
  }

  .back-btn {
    padding: 6px 10px;
    font-size: 12px;
  }

  .progress {
    min-width: 100px;
  }

  .card-container {
    margin: 24px 0;
  }

  #kanjiDisplay {
    font-size: 48px;
  }

  #yomikataDisplay {
    font-size: 14px;
    margin: 16px 0 6px 0;
  }

  #artiDisplay {
    font-size: 13px;
  }

  .front p,
  .back p {
    font-size: 12px;
  }

  .controls {
    gap: 6px;
    margin: 20px 0;
  }

  .btn-nav {
    padding: 8px 14px;
    font-size: 12px;
  }

  .counter {
    padding: 8px 14px;
    font-size: 12px;
    min-width: 90px;
  }

  .card-info {
    font-size: 11px;
    margin-top: 12px;
  }
}

/* ============================================================================
   UTILITY
   ========================================================================== */

::-webkit-scrollbar {
  width: 8px;
}

::-webkit-scrollbar-track {
  background: transparent;
}

::-webkit-scrollbar-thumb {
  background: #d0d0d0;
  border-radius: 4px;
}

::-webkit-scrollbar-thumb:hover {
  background: #999;
}

@media (prefers-color-scheme: dark) {
  ::-webkit-scrollbar-thumb {
    background: #444;
  }

  ::-webkit-scrollbar-thumb:hover {
    background: #666;
  }
}