/* CSS Variables */
:root {
  --bg-primary: #0f0f12;
  --bg-secondary: #1a1a21;
  --bg-tertiary: #252530;
  --text-primary: #f0f0f5;
  --text-secondary: #9090a0;
  --text-muted: #606070;
  --accent: #e8c547;
  --accent-hover: #f5d668;
  --accent-dim: #b39830;
  --success: #4ade80;
  --error: #f87171;
  --error-bg: rgba(248, 113, 113, 0.1);
  --success-bg: rgba(74, 222, 128, 0.1);
  --border: #2a2a35;
  --shadow: rgba(0, 0, 0, 0.4);
  --font-chinese: 'Noto Sans SC', 'Microsoft YaHei', 'PingFang SC', sans-serif;
  --font-mono: 'Space Mono', 'Consolas', monospace;
}

/* Reset & Base */
*, *::before, *::after {
  box-sizing: border-box;
  margin: 0;
  padding: 0;
}

html {
  font-size: 16px;
}

body {
  font-family: var(--font-mono);
  background: var(--bg-primary);
  color: var(--text-primary);
  min-height: 100vh;
  line-height: 1.6;
  background-image:
    radial-gradient(ellipse at 20% 0%, rgba(232, 197, 71, 0.03) 0%, transparent 50%),
    radial-gradient(ellipse at 80% 100%, rgba(232, 197, 71, 0.02) 0%, transparent 50%);
}

/* App Container */
.app {
  min-height: 100vh;
  display: flex;
  flex-direction: column;
}

/* Screens */
.screen {
  flex: 1;
  display: flex;
  flex-direction: column;
  padding: 1.5rem;
  max-width: 800px;
  margin: 0 auto;
  width: 100%;
}

.screen.hidden {
  display: none;
}

/* Menu Screen */
.header {
  text-align: center;
  padding: 2rem 0 3rem;
}

.title {
  font-family: var(--font-chinese);
  font-size: 3.5rem;
  font-weight: 700;
  color: var(--accent);
  letter-spacing: 0.1em;
  text-shadow: 0 0 40px rgba(232, 197, 71, 0.3);
  margin-bottom: 0.5rem;
}

.subtitle {
  font-size: 1rem;
  color: var(--text-secondary);
  text-transform: uppercase;
  letter-spacing: 0.3em;
}

/* Mode Toggle */
.mode-toggle-container {
  margin-top: 2rem;
  display: flex;
  justify-content: center;
}

.mode-toggle {
  display: flex;
  align-items: center;
  gap: 0.75rem;
  cursor: pointer;
  user-select: none;
}

.mode-toggle input[type="checkbox"] {
  display: none;
}

.toggle-slider {
  position: relative;
  width: 48px;
  height: 24px;
  background: var(--bg-tertiary);
  border: 1px solid var(--border);
  border-radius: 12px;
  transition: all 0.3s ease;
}

.toggle-slider::before {
  content: '';
  position: absolute;
  width: 18px;
  height: 18px;
  border-radius: 50%;
  background: var(--text-muted);
  top: 2px;
  left: 2px;
  transition: all 0.3s ease;
}

.mode-toggle input[type="checkbox"]:checked + .toggle-slider {
  background: var(--accent);
  border-color: var(--accent);
}

.mode-toggle input[type="checkbox"]:checked + .toggle-slider::before {
  transform: translateX(24px);
  background: var(--bg-primary);
}

.toggle-label {
  font-family: var(--font-mono);
  font-size: 0.875rem;
  color: var(--text-secondary);
  transition: color 0.2s ease;
}

.mode-toggle:hover .toggle-label {
  color: var(--text-primary);
}

/* Exercise Grid */
.exercise-grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(140px, 1fr));
  gap: 1rem;
  padding: 1rem 0;
  flex: 1;
  align-content: start;
}

.exercise-btn {
  font-family: var(--font-mono);
  background: var(--bg-secondary);
  border: 1px solid var(--border);
  border-radius: 8px;
  padding: 1.25rem 1rem;
  color: var(--text-primary);
  cursor: pointer;
  transition: all 0.2s ease;
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: 0.5rem;
}

.exercise-btn:hover {
  background: var(--bg-tertiary);
  border-color: var(--accent-dim);
  transform: translateY(-2px);
}

.exercise-btn:active {
  transform: translateY(0);
}

.exercise-btn .range {
  font-size: 1rem;
  font-weight: 700;
}

.exercise-btn .progress {
  font-size: 0.75rem;
  color: var(--text-muted);
}

.exercise-btn.completed {
  border-color: var(--success);
  background: var(--success-bg);
}

.exercise-btn.completed .progress {
  color: var(--success);
}

/* Menu Footer */
.menu-footer {
  text-align: center;
  padding: 2rem 0;
  border-top: 1px solid var(--border);
  margin-top: 2rem;
}

.menu-footer p {
  color: var(--text-muted);
  font-size: 0.875rem;
  margin-bottom: 1rem;
}

.reset-btn {
  font-family: var(--font-mono);
  background: transparent;
  border: 1px solid var(--error);
  color: var(--error);
  padding: 0.5rem 1rem;
  border-radius: 4px;
  cursor: pointer;
  font-size: 0.75rem;
  text-transform: uppercase;
  letter-spacing: 0.1em;
  transition: all 0.2s ease;
}

.reset-btn:hover {
  background: var(--error-bg);
}

/* Practice Screen */
.practice-header {
  display: flex;
  justify-content: space-between;
  align-items: center;
  padding-bottom: 1rem;
  border-bottom: 1px solid var(--border);
}

.back-btn {
  font-family: var(--font-mono);
  background: transparent;
  border: none;
  color: var(--text-secondary);
  cursor: pointer;
  font-size: 0.875rem;
  padding: 0.5rem;
  transition: color 0.2s ease;
}

.back-btn:hover {
  color: var(--accent);
}

.progress-info {
  display: flex;
  align-items: baseline;
  gap: 0.5rem;
}

#progress-text {
  font-size: 1.25rem;
  font-weight: 700;
  color: var(--accent);
}

.mastered-label {
  font-size: 0.75rem;
  color: var(--text-muted);
  text-transform: uppercase;
}

/* Practice Main */
.practice-main {
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: flex-start;
  padding-top: 10vh;
  padding-bottom: 50vh;
  gap: 1.5rem;
}

/* Character Display */
.character-display {
  width: 200px;
  height: 200px;
  display: flex;
  align-items: center;
  justify-content: center;
  background: var(--bg-secondary);
  border: 2px solid var(--border);
  border-radius: 16px;
  box-shadow: 0 8px 32px var(--shadow);
}

.character {
  font-family: var(--font-chinese);
  font-size: 8rem;
  font-weight: 700;
  color: var(--text-primary);
  line-height: 1;
}

/* Feedback */
.feedback-container {
  height: 2.75rem;
  position: relative;
}

.feedback,
.hint-display {
  position: absolute;
  left: 50%;
  top: 50%;
  transform: translate(-50%, -50%);
  white-space: nowrap;
}

.feedback {
  font-size: 1.5rem;
  font-weight: 700;
  padding: 0.5rem 1rem;
  border-radius: 4px;
  opacity: 0;
  transition: opacity 0.2s ease;
}

.feedback.show {
  opacity: 1;
}

.feedback.correct {
  color: var(--success);
  background: var(--success-bg);
}

.feedback.incorrect {
  color: var(--error);
  background: var(--error-bg);
}

.hint-display {
  font-size: 1.5rem;
  color: var(--accent);
  font-weight: 700;
  opacity: 1;
  transition: opacity 0.2s ease;
}

.hint-display.hidden {
  opacity: 0;
}

/* Input Container */
.input-container {
  display: flex;
  gap: 1rem;
  width: 100%;
  max-width: 400px;
}

.pinyin-input {
  flex: 1;
  font-family: var(--font-mono);
  font-size: 1.25rem;
  background: var(--bg-secondary);
  border: 2px solid var(--border);
  border-radius: 8px;
  padding: 1rem 1.25rem;
  color: var(--text-primary);
  outline: none;
  transition: border-color 0.2s ease;
}

.pinyin-input:focus {
  border-color: var(--accent);
}

.pinyin-input::placeholder {
  color: var(--text-muted);
}

.pinyin-input.error {
  border-color: var(--error);
  animation: shake 0.4s ease;
}

@keyframes shake {
  0%, 100% { transform: translateX(0); }
  20%, 60% { transform: translateX(-8px); }
  40%, 80% { transform: translateX(8px); }
}

.hint-btn {
  display: none;
  font-family: var(--font-mono);
  background: var(--bg-tertiary);
  border: 1px solid var(--border);
  color: var(--text-secondary);
  padding: 1rem 1.25rem;
  border-radius: 8px;
  cursor: pointer;
  font-size: 0.875rem;
  white-space: nowrap;
  transition: all 0.2s ease;
}

.hint-btn:hover {
  background: var(--accent-dim);
  border-color: var(--accent);
  color: var(--bg-primary);
}

/* Streak Info */
.streak-info {
  color: var(--text-muted);
  font-size: 0.875rem;
}

#streak-text {
  color: var(--text-secondary);
}

/* Modal */
.modal {
  position: fixed;
  inset: 0;
  background: rgba(0, 0, 0, 0.8);
  display: flex;
  align-items: center;
  justify-content: center;
  padding: 1rem;
  z-index: 100;
}

.modal.hidden {
  display: none;
}

.modal-content {
  background: var(--bg-secondary);
  border: 1px solid var(--border);
  border-radius: 16px;
  padding: 3rem;
  text-align: center;
  max-width: 400px;
  width: 100%;
}

.modal-content h2 {
  font-size: 1.5rem;
  margin-bottom: 1rem;
  color: var(--accent);
}

.modal-content p {
  color: var(--text-secondary);
  margin-bottom: 2rem;
}

.modal-btn {
  font-family: var(--font-mono);
  background: var(--accent);
  border: none;
  color: var(--bg-primary);
  padding: 1rem 2rem;
  border-radius: 8px;
  cursor: pointer;
  font-size: 1rem;
  font-weight: 700;
  transition: background 0.2s ease;
}

.modal-btn:hover {
  background: var(--accent-hover);
}

.modal-link-btn {
  display: block;
  margin: 1rem auto 0;
  font-family: var(--font-mono);
  background: transparent;
  border: none;
  color: var(--text-muted);
  padding: 0.5rem 1rem;
  cursor: pointer;
  font-size: 0.875rem;
  transition: color 0.2s ease;
  text-decoration: underline;
  text-underline-offset: 3px;
}

.modal-link-btn:hover {
  color: var(--text-secondary);
}

/* Responsive */
@media (max-width: 600px) {
  .title {
    font-size: 2.5rem;
  }

  .exercise-grid {
    grid-template-columns: repeat(2, 1fr);
  }

  .practice-main {
    padding-top: 2vh;
    padding-bottom: 55vh;
    gap: 0.75rem;
  }

  .feedback-container {
    height: 2.5rem;
  }

  .character-display {
    width: 120px;
    height: 120px;
  }

  .character {
    font-size: 4.5rem;
  }

  .input-container {
    flex-direction: column;
  }

  .hint-btn {
    width: 100%;
  }
}

@media (max-width: 400px) {
  .screen {
    padding: 1rem;
  }

  .title {
    font-size: 2rem;
  }

  .exercise-grid {
    grid-template-columns: repeat(2, 1fr);
    gap: 0.75rem;
  }

  .exercise-btn {
    padding: 1rem 0.75rem;
  }
}