/* ==========================================================================
   한자 퀴즈 - Base Stylesheet
   Mobile-first responsive design: 320px minimum → 1920px maximum
   Dark/Light mode with CSS custom properties
   Requirements: 6.1 (64px+ Hanja), 6.3 (no horizontal scroll), 6.4 (44×44px buttons, 8px gap)
   ========================================================================== */

/* ==========================================================================
   Theme Variables - Light Mode (default)
   ========================================================================== */

:root {
  /* Background */
  --bg-primary: #f0f4f8;
  --bg-card: #ffffff;
  --bg-card-border: #e2e8f0;
  --bg-card-shadow: rgba(0, 0, 0, 0.1);
  --bg-card-shadow-sm: rgba(0, 0, 0, 0.08);

  /* Text */
  --text-primary: #333333;
  --text-secondary: #555555;
  --text-heading: #1a237e;
  --text-muted: #666666;
  --text-answer: #222222;

  /* Grade Buttons */
  --btn-grade-bg: #e3f2fd;
  --btn-grade-border: #bbdefb;
  --btn-grade-text: #1a237e;
  --btn-grade-hover-bg: #bbdefb;
  --btn-grade-hover-border: #90caf9;
  --btn-grade-active-bg: #1a237e;
  --btn-grade-active-border: #1a237e;
  --btn-grade-active-text: #ffffff;
  --btn-grade-annotation: #666666;
  --btn-grade-active-annotation: #bbdefb;

  /* Quiz Controls */
  --btn-reveal-bg: #4caf50;
  --btn-reveal-hover: #388e3c;
  --btn-next-bg: #1976d2;
  --btn-next-hover: #1565c0;

  /* Error */
  --error-text: #c62828;
  --error-btn-border: #c62828;
  --error-btn-hover-bg: #ffebee;
  --error-btn-bg: #ffffff;

  /* Focus */
  --focus-color: #1976d2;

  /* Theme toggle */
  --btn-theme-bg: transparent;
  --btn-theme-border: #ccc;
}

/* ==========================================================================
   Theme Variables - Dark Mode
   ========================================================================== */

[data-theme="dark"] {
  --bg-primary: #121212;
  --bg-card: #1e1e1e;
  --bg-card-border: #333333;
  --bg-card-shadow: rgba(0, 0, 0, 0.4);
  --bg-card-shadow-sm: rgba(0, 0, 0, 0.3);

  --text-primary: #e0e0e0;
  --text-secondary: #b0b0b0;
  --text-heading: #90caf9;
  --text-muted: #9e9e9e;
  --text-answer: #f0f0f0;

  --btn-grade-bg: #263238;
  --btn-grade-border: #37474f;
  --btn-grade-text: #90caf9;
  --btn-grade-hover-bg: #37474f;
  --btn-grade-hover-border: #546e7a;
  --btn-grade-active-bg: #1565c0;
  --btn-grade-active-border: #1565c0;
  --btn-grade-active-text: #ffffff;
  --btn-grade-annotation: #9e9e9e;
  --btn-grade-active-annotation: #bbdefb;

  --btn-reveal-bg: #2e7d32;
  --btn-reveal-hover: #1b5e20;
  --btn-next-bg: #1565c0;
  --btn-next-hover: #0d47a1;

  --error-text: #ef5350;
  --error-btn-border: #ef5350;
  --error-btn-hover-bg: #2c1a1a;
  --error-btn-bg: #1e1e1e;

  --focus-color: #90caf9;

  --btn-theme-bg: transparent;
  --btn-theme-border: #555;
}

/* Auto dark mode (system preference) - applied when no explicit theme set */
@media (prefers-color-scheme: dark) {
  :root:not([data-theme="light"]) {
    --bg-primary: #121212;
    --bg-card: #1e1e1e;
    --bg-card-border: #333333;
    --bg-card-shadow: rgba(0, 0, 0, 0.4);
    --bg-card-shadow-sm: rgba(0, 0, 0, 0.3);

    --text-primary: #e0e0e0;
    --text-secondary: #b0b0b0;
    --text-heading: #90caf9;
    --text-muted: #9e9e9e;
    --text-answer: #f0f0f0;

    --btn-grade-bg: #263238;
    --btn-grade-border: #37474f;
    --btn-grade-text: #90caf9;
    --btn-grade-hover-bg: #37474f;
    --btn-grade-hover-border: #546e7a;
    --btn-grade-active-bg: #1565c0;
    --btn-grade-active-border: #1565c0;
    --btn-grade-active-text: #ffffff;
    --btn-grade-annotation: #9e9e9e;
    --btn-grade-active-annotation: #bbdefb;

    --btn-reveal-bg: #2e7d32;
    --btn-reveal-hover: #1b5e20;
    --btn-next-bg: #1565c0;
    --btn-next-hover: #0d47a1;

    --error-text: #ef5350;
    --error-btn-border: #ef5350;
    --error-btn-hover-bg: #2c1a1a;
    --error-btn-bg: #1e1e1e;

    --focus-color: #90caf9;

    --btn-theme-bg: transparent;
    --btn-theme-border: #555;
  }
}

/* ==========================================================================
   Reset and Base
   ========================================================================== */

*,
*::before,
*::after {
  box-sizing: border-box;
  margin: 0;
  padding: 0;
}

html {
  font-size: 16px;
  overflow-x: hidden;
}

body {
  font-family: 'Noto Sans KR', -apple-system, BlinkMacSystemFont, 'Malgun Gothic', sans-serif;
  line-height: 1.5;
  color: var(--text-primary);
  background-color: var(--bg-primary);
  min-width: 320px;
  max-width: 100vw;
  overflow-x: hidden;
  padding: 16px;
  transition: background-color 0.3s, color 0.3s;
}

/* ==========================================================================
   Header & Theme Toggle & Menu Button
   ========================================================================== */

header {
  display: flex;
  align-items: center;
  justify-content: space-between;
  margin-bottom: 24px;
  position: relative;
}

header h1 {
  font-size: 1.5rem;
  color: var(--text-heading);
  flex: 1;
  text-align: center;
}

.btn-menu {
  width: 44px;
  height: 44px;
  font-size: 1.5rem;
  border: none;
  border-radius: 8px;
  background: transparent;
  color: var(--text-primary);
  cursor: pointer;
  transition: background-color 0.2s;
  touch-action: manipulation;
  flex-shrink: 0;
}

.btn-menu:hover {
  background-color: var(--btn-grade-hover-bg);
}

#btn-theme {
  width: 44px;
  height: 44px;
  font-size: 1.25rem;
  border: 2px solid var(--btn-theme-border);
  border-radius: 50%;
  background: var(--btn-theme-bg);
  cursor: pointer;
  transition: border-color 0.2s, transform 0.1s;
  touch-action: manipulation;
  flex-shrink: 0;
}

#btn-theme:hover {
  border-color: var(--focus-color);
}

#btn-theme:active {
  transform: scale(0.9);
}

#btn-theme:focus-visible {
  outline: 3px solid var(--focus-color);
  outline-offset: 2px;
}

/* ==========================================================================
   Slide-out Grade Menu
   ========================================================================== */

.menu-overlay {
  position: fixed;
  inset: 0;
  background-color: rgba(0, 0, 0, 0.4);
  z-index: 999;
  transition: opacity 0.3s;
}

.menu-overlay.hidden {
  display: none !important;
}

.grade-menu {
  position: fixed;
  top: 0;
  left: -300px;
  width: 280px;
  max-width: 80vw;
  height: 100vh;
  background-color: var(--bg-card);
  border-right: 1px solid var(--bg-card-border);
  box-shadow: 4px 0 16px rgba(0, 0, 0, 0.15);
  z-index: 1000;
  overflow-y: auto;
  padding: 20px 16px;
  transition: left 0.3s ease;
}

.grade-menu.open {
  left: 0;
}

.grade-menu-header {
  display: flex;
  align-items: center;
  justify-content: space-between;
  margin-bottom: 16px;
}

.grade-menu-header h2 {
  font-size: 1.125rem;
  color: var(--text-heading);
  margin: 0;
}

.btn-menu-close {
  width: 36px;
  height: 36px;
  font-size: 1.2rem;
  border: none;
  border-radius: 50%;
  background: transparent;
  color: var(--text-primary);
  cursor: pointer;
  transition: background-color 0.2s;
}

.btn-menu-close:hover {
  background-color: var(--btn-grade-hover-bg);
}

/* ==========================================================================
   Main Container
   ========================================================================== */

main {
  max-width: 800px;
  margin: 0 auto;
  width: 100%;
}

/* ==========================================================================
   Grade Selector (inside menu)
   ========================================================================== */

#grade-selector {
  margin-bottom: 32px;
}

#grade-selector h2 {
  font-size: 1.125rem;
  margin-bottom: 12px;
  color: var(--text-secondary);
  text-align: center;
}

.grade-buttons {
  display: flex;
  flex-direction: column;
  gap: 6px;
}

.grade-buttons button {
  width: 100%;
  min-height: 44px;
  padding: 10px 12px;
  font-size: 0.9rem;
  font-weight: 500;
  border: 2px solid var(--btn-grade-border);
  border-radius: 8px;
  background-color: var(--btn-grade-bg);
  color: var(--btn-grade-text);
  cursor: pointer;
  transition: background-color 0.2s, border-color 0.2s, transform 0.1s;
  touch-action: manipulation;
  text-align: left;
}

.grade-buttons button:focus-visible {
  outline: 3px solid var(--focus-color);
  outline-offset: 2px;
}

.grade-buttons button:hover {
  background-color: var(--btn-grade-hover-bg);
  border-color: var(--btn-grade-hover-border);
}

.grade-buttons button:active {
  transform: scale(0.96);
}

.grade-buttons button.active {
  background-color: var(--btn-grade-active-bg);
  border-color: var(--btn-grade-active-border);
  color: var(--btn-grade-active-text);
  font-weight: 700;
}

/* 1급II annotation styling */
.grade-buttons button .annotation {
  display: block;
  font-size: 0.7rem;
  font-weight: 400;
  color: var(--btn-grade-annotation);
  margin-top: 2px;
}

.grade-buttons button.active .annotation {
  color: var(--btn-grade-active-annotation);
}

/* ==========================================================================
   Quiz Area
   ========================================================================== */

#quiz-area {
  text-align: center;
}

.current-grade-info {
  display: flex;
  align-items: center;
  justify-content: space-between;
  margin-bottom: 16px;
}

.current-grade-left {
  font-size: 1.1rem;
  color: var(--text-heading);
  font-weight: 600;
}

.current-grade-info #grade-annotation {
  font-size: 0.85rem;
  font-weight: 400;
  color: var(--text-muted);
  margin-left: 8px;
}

.character-card {
  background: var(--bg-card);
  border: 1px solid var(--bg-card-border);
  border-radius: 16px;
  padding: 32px 0px;
  margin-bottom: 24px;
  box-shadow: 0 2px 8px var(--bg-card-shadow);
  transition: background-color 0.3s, box-shadow 0.3s;
  position: relative;
}

.character-card-inner {
  position: relative;
  display: flex;
  align-items: center;
  justify-content: center;
  min-height: 120px;
}

.hanja-area {
  display: flex;
  align-items: center;
  justify-content: center;
}

/* Hanja character display - minimum 64px per Req 6.1 */
.hanja-display {
  font-size: 80px;
  line-height: 1.2;
  font-weight: 400;
  color: var(--text-heading);
}

/* Answer details area - absolutely positioned to the right */
.answer-area-inline {
  text-align: left;
  min-width: 120px;
}

.answer-area-inline.hidden {
  display: none !important;
}

.answer-area-inline:not(.hidden) {
  position: absolute;
  right: 16px;
  top: 50%;
  transform: translateY(-50%);
  padding: 12px 16px;
  padding-left: 20px;
  border-left: 2px solid var(--bg-card-border);
}

.answer-meaning-text {
  font-size: 1.2rem;
  font-weight: 600;
  color: var(--text-answer);
  margin-bottom: 8px;
}

.answer-radical-line {
  font-size: 1rem;
  color: var(--text-secondary);
}

.answer-radical-line .answer-label {
  font-weight: 600;
  margin-right: 4px;
}

.answer-details dt {
  font-weight: 600;
  font-size: 0.85rem;
  color: var(--text-secondary);
}

.answer-details dd {
  color: var(--text-answer);
  font-size: 0.95rem;
}

/* ==========================================================================
   Quiz Controls
   ========================================================================== */

.quiz-controls {
  display: flex;
  flex-wrap: wrap;
  gap: 8px;
  justify-content: center;
  margin-top: 16px;
}

.quiz-controls button {
  min-width: 44px;
  min-height: 44px;
  padding: 12px 24px;
  font-size: 1rem;
  font-weight: 600;
  border: none;
  border-radius: 10px;
  cursor: pointer;
  transition: background-color 0.2s, transform 0.1s;
  touch-action: manipulation;
  color: #ffffff;
}

.quiz-controls button:focus-visible {
  outline: 3px solid var(--focus-color);
  outline-offset: 2px;
}

.quiz-controls button:disabled {
  opacity: 0.5;
  cursor: not-allowed;
}

#btn-reveal {
  background-color: var(--btn-reveal-bg);
}

#btn-reveal:hover:not(:disabled) {
  background-color: var(--btn-reveal-hover);
}

#btn-reveal:active:not(:disabled) {
  transform: scale(0.96);
}

#btn-next {
  background-color: var(--btn-next-bg);
}

#btn-next:hover:not(:disabled) {
  background-color: var(--btn-next-hover);
}

#btn-next:active:not(:disabled) {
  transform: scale(0.96);
}

/* ==========================================================================
   Error Container
   ========================================================================== */

#error-container {
  text-align: center;
  padding: 32px 16px;
}

#error-message {
  font-size: 1rem;
  color: var(--error-text);
  margin-bottom: 16px;
}

#btn-retry {
  min-width: 44px;
  min-height: 44px;
  padding: 12px 24px;
  font-size: 1rem;
  font-weight: 600;
  border: 2px solid var(--error-btn-border);
  border-radius: 10px;
  background-color: var(--error-btn-bg);
  color: var(--error-text);
  cursor: pointer;
  transition: background-color 0.2s;
  touch-action: manipulation;
}

#btn-retry:focus-visible {
  outline: 3px solid var(--error-text);
  outline-offset: 2px;
}

#btn-retry:hover {
  background-color: var(--error-btn-hover-bg);
}

/* ==========================================================================
   Utility Classes
   ========================================================================== */

.hidden {
  display: none !important;
}

/* Initial guide */
#initial-guide {
  text-align: center;
  padding: 80px 16px;
}

.guide-text {
  font-size: 1.1rem;
  color: var(--text-muted);
}

/* ==========================================================================
   Bookmark (오답 체크) & Review Controls
   ========================================================================== */

.btn-bookmark {
  position: absolute;
  bottom: 12px;
  right: 12px;
  width: 36px;
  height: 36px;
  padding: 0;
  font-size: 1rem;
  line-height: 36px;
  text-align: center;
  border: 2px solid #d1d5db;
  border-radius: 50%;
  background-color: var(--bg-card);
  color: #9ca3af;
  cursor: pointer;
  transition: transform 0.2s, border-color 0.2s, background-color 0.2s, color 0.2s;
  touch-action: manipulation;
}

.btn-bookmark:hover {
  border-color: #f97316;
  color: #f97316;
}

[data-theme="dark"] .btn-bookmark {
  border-color: #4b5563;
  color: #6b7280;
  background-color: #1e1e1e;
}

[data-theme="dark"] .btn-bookmark:hover {
  border-color: #f97316;
  color: #fb923c;
}

.btn-bookmark:active {
  transform: scale(0.85);
}

.btn-bookmark.bookmarked {
  border-color: #f97316;
  background-color: #f97316;
  color: #ffffff;
}

[data-theme="dark"] .btn-bookmark.bookmarked {
  background-color: #ea580c;
  border-color: #f97316;
  color: #ffffff;
}

.review-controls {
  display: flex;
  gap: 8px;
  align-items: center;
  flex-wrap: wrap;
}

.btn-review {
  min-width: auto;
  min-height: 32px;
  padding: 6px 12px;
  font-size: 0.8rem;
  font-weight: 600;
  border: 2px solid #f59e0b;
  border-radius: 10px;
  background-color: var(--bg-card);
  color: #f59e0b;
  cursor: pointer;
  transition: background-color 0.2s, transform 0.1s;
  touch-action: manipulation;
}

.btn-review:hover:not(:disabled) {
  background-color: #fef3c7;
}

[data-theme="dark"] .btn-review:hover:not(:disabled) {
  background-color: #422006;
}

.btn-review:disabled {
  opacity: 0.4;
  cursor: not-allowed;
}

.btn-review:active:not(:disabled) {
  transform: scale(0.96);
}

.btn-review-exit {
  min-width: auto;
  min-height: 32px;
  padding: 6px 12px;
  font-size: 0.8rem;
  font-weight: 600;
  border: 2px solid var(--btn-grade-border);
  border-radius: 10px;
  background-color: var(--bg-card);
  color: var(--text-primary);
  cursor: pointer;
  transition: background-color 0.2s, transform 0.1s;
  touch-action: manipulation;
}

.btn-review-exit:hover {
  background-color: var(--btn-grade-hover-bg);
}

.btn-review-exit:active {
  transform: scale(0.96);
}

/* Review mode indicator */
.review-mode-badge {
  display: inline-block;
  background-color: #f59e0b;
  color: #ffffff;
  font-size: 0.75rem;
  font-weight: 700;
  padding: 2px 8px;
  border-radius: 4px;
  margin-left: 8px;
  vertical-align: middle;
}

/* ==========================================================================
   Responsive: Tablet (≥600px)
   ========================================================================== */

@media (min-width: 600px) {
  body {
    padding: 24px;
  }

  header h1 {
    font-size: 2rem;
  }

  .grade-buttons button {
    padding: 10px 16px;
    font-size: 1rem;
  }

  .hanja-display {
    font-size: 96px;
  }

  .character-card {
    padding: 48px 24px;
  }

  .quiz-controls button {
    padding: 14px 32px;
    font-size: 1.1rem;
  }
}

/* ==========================================================================
   Responsive: Desktop (≥1024px)
   ========================================================================== */

@media (min-width: 1024px) {
  body {
    padding: 32px;
  }

  header h1 {
    font-size: 2.25rem;
  }

  .hanja-display {
    font-size: 120px;
  }

  .character-card {
    padding: 56px 32px;
  }

  #grade-selector {
    margin-bottom: 40px;
  }
}

/* ==========================================================================
   Responsive: Large Desktop (≥1440px)
   ========================================================================== */

@media (min-width: 1440px) {
  main {
    max-width: 900px;
  }

  .hanja-display {
    font-size: 140px;
  }
}