/* ================================
   CSS Variables & Themes
   ================================ */
:root {
  /* Colors - Dark Theme (Default) */
  --bg: #0a0a0a;
  --bg-secondary: #12121a;
  --text: #fafafa;
  --text-muted: #71717a;
  --accent: #8b5cf6;
  --border: #2a2a3a;

  /* Transitions */
  --transition-speed: 0.3s;
}

[data-theme="light"] {
  --bg: #fafafa;
  --bg-secondary: #e5e5e5;
  --text: #0a0a0a;
  --text-muted: #525252;
  --accent: #7c3aed;
  --border: #d4d4d4;
}

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

html {
  font-size: 16px;
}

body {
  font-family: 'SF Mono', 'Roboto Mono', 'Fira Code', monospace;
  background: var(--bg);
  color: var(--text);
  min-height: 100vh;
  display: flex;
  flex-direction: column;
  transition: background var(--transition-speed), color var(--transition-speed);
}

/* ================================
   Typography
   ================================ */
h1 {
  font-weight: 400;
  letter-spacing: 0.2em;
}

/* ================================
   Layout
   ================================ */
.header {
  display: flex;
  justify-content: space-between;
  align-items: center;
  padding: 1.5rem 2rem;
}

.main {
  flex: 1;
  display: flex;
  justify-content: center;
  align-items: center;
  padding: 2rem;
}

.controls-section {
  padding: 2rem;
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: 1.5rem;
}

.footer {
  padding: 1rem 2rem;
  text-align: center;
  color: var(--text-muted);
  font-size: 0.875rem;
  user-select: none;
}

/* ================================
   Header Controls
   ================================ */
.controls-left {
  display: flex;
  gap: 0.75rem;
}

.title {
  font-size: 1rem;
  color: var(--text-muted);
}

.control-btn {
  width: 2.5rem;
  height: 2.5rem;
  border-radius: 50%;
  border: 1px solid var(--border);
  background: transparent;
  color: var(--text);
  cursor: pointer;
  display: flex;
  align-items: center;
  justify-content: center;
  font-size: 1.25rem;
  transition: all var(--transition-speed);
  user-select: none;
}

.control-btn:hover {
  border-color: var(--text);
}

.control-btn:focus {
  outline: 2px solid var(--accent);
  outline-offset: 2px;
}

/* Theme toggle icons */
#theme-toggle .icon-moon {
  display: none;
}

[data-theme="light"] #theme-toggle .icon-sun {
  display: none;
}

[data-theme="light"] #theme-toggle .icon-moon {
  display: inline;
}

/* Sound toggle icons */
#sound-toggle .icon-muted {
  display: none;
}

#sound-toggle.muted .icon-sound {
  display: none;
}

#sound-toggle.muted .icon-muted {
  display: inline;
}

/* ================================
   Word Display (Serial Mode)
   ================================ */
.word-display {
  font-size: 4rem;
  font-weight: 300;
  text-align: center;
  min-height: 6rem;
  display: flex;
  align-items: center;
  justify-content: center;
}

#current-word {
  transition: opacity 0.05s;
}

/* ================================
   Highlight Mode
   ================================ */
.highlight-display {
  width: 100%;
  max-width: 700px;
  padding: 2rem;
  text-align: center;
}

.highlight-display p {
  font-size: 1.5rem;
  line-height: 2;
  color: var(--text-muted);
}

.highlight-display .current-word {
  color: var(--text);
  font-weight: 600;
  background: var(--bg-secondary);
  padding: 0.1em 0.3em;
  border-radius: 4px;
}

/* ================================
   Scroll Mode
   ================================ */
.scroll-display {
  width: 100%;
  max-width: 700px;
  height: 300px;
  overflow: hidden;
  position: relative;
  mask-image: linear-gradient(
    to bottom,
    transparent 0%,
    black 20%,
    black 80%,
    transparent 100%
  );
  -webkit-mask-image: linear-gradient(
    to bottom,
    transparent 0%,
    black 20%,
    black 80%,
    transparent 100%
  );
}

#scroll-text {
  font-size: 1.25rem;
  line-height: 2;
  text-align: center;
  padding: 2rem;
  transition: transform 0.1s linear;
}

#scroll-text .current-line {
  color: var(--text);
  font-weight: 500;
}

#scroll-text .past-line {
  color: var(--text-muted);
  opacity: 0.5;
}

#scroll-text .future-line {
  color: var(--text-muted);
}

#scroll-text .scroll-line {
  padding: 0.25rem 0;
  transition: all 0.2s ease;
}

/* ================================
   Mode Selector
   ================================ */
.mode-selector {
  display: flex;
  align-items: center;
  gap: 0.75rem;
}

.mode-label {
  color: var(--text-muted);
  font-size: 0.875rem;
}

.mode-select {
  padding: 0.5rem 2rem 0.5rem 1rem;
  border: 1px solid var(--border);
  background: var(--bg);
  color: var(--text);
  font-family: inherit;
  font-size: 0.875rem;
  cursor: pointer;
  transition: all var(--transition-speed);
  appearance: none;
  -webkit-appearance: none;
  background-image: url("data:image/svg+xml,%3Csvg xmlns='http://www.w3.org/2000/svg' width='12' height='12' viewBox='0 0 12 12'%3E%3Cpath fill='%2371717a' d='M6 8L1 3h10z'/%3E%3C/svg%3E");
  background-repeat: no-repeat;
  background-position: right 0.75rem center;
}

.mode-select:hover {
  border-color: var(--text);
}

.mode-select:focus {
  outline: 2px solid var(--accent);
  outline-offset: 2px;
}

/* Hidden utility class */
.hidden {
  display: none !important;
}

/* ================================
   Speed Presets
   ================================ */
.speed-presets {
  display: flex;
  gap: 0.75rem;
}

.preset-btn {
  padding: 0.5rem 1.25rem;
  border: 1px solid var(--border);
  background: transparent;
  color: var(--text);
  font-family: inherit;
  font-size: 0.875rem;
  cursor: pointer;
  transition: all var(--transition-speed);
  user-select: none;
}

.preset-btn:hover {
  border-color: var(--text);
}

.preset-btn:focus {
  outline: 2px solid var(--accent);
  outline-offset: 2px;
}

.preset-btn.active {
  background: var(--text);
  color: var(--bg);
}

/* ================================
   Speed Slider
   ================================ */
.speed-slider-container {
  display: flex;
  align-items: center;
  gap: 1rem;
  width: 100%;
  max-width: 400px;
}

#speed-slider {
  flex: 1;
  height: 4px;
  -webkit-appearance: none;
  appearance: none;
  background: var(--border);
  border-radius: 2px;
  cursor: pointer;
}

#speed-slider::-webkit-slider-thumb {
  -webkit-appearance: none;
  appearance: none;
  width: 16px;
  height: 16px;
  background: var(--text);
  border-radius: 50%;
  cursor: pointer;
  transition: transform var(--transition-speed);
}

#speed-slider::-webkit-slider-thumb:hover {
  transform: scale(1.2);
}

#speed-slider::-moz-range-thumb {
  width: 16px;
  height: 16px;
  background: var(--text);
  border: none;
  border-radius: 50%;
  cursor: pointer;
}

#speed-slider:focus {
  outline: none;
}

#speed-slider:focus::-webkit-slider-thumb {
  box-shadow: 0 0 0 3px var(--accent);
}

.speed-display {
  min-width: 80px;
  text-align: right;
  font-size: 0.875rem;
  color: var(--text-muted);
}

/* ================================
   Playback Controls
   ================================ */
.playback-controls {
  display: flex;
  gap: 1rem;
}

.playback-btn {
  display: flex;
  align-items: center;
  gap: 0.5rem;
  padding: 0.75rem 1.5rem;
  border: 1px solid var(--border);
  background: transparent;
  color: var(--text);
  font-family: inherit;
  font-size: 1rem;
  cursor: pointer;
  transition: all var(--transition-speed);
  user-select: none;
}

.playback-btn:hover {
  border-color: var(--text);
}

.playback-btn:focus {
  outline: 2px solid var(--accent);
  outline-offset: 2px;
}

/* Play/Pause state */
#play-btn .icon-pause,
#play-btn .text-pause {
  display: none;
}

#play-btn.playing .icon-play,
#play-btn.playing .text-play {
  display: none;
}

#play-btn.playing .icon-pause,
#play-btn.playing .text-pause {
  display: inline;
}

/* ================================
   Progress
   ================================ */
.progress-container {
  color: var(--text-muted);
  font-size: 0.875rem;
}

/* ================================
   Book Selection
   ================================ */
.book-selection {
  padding: 1.5rem 2rem;
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: 1rem;
  border-bottom: 1px solid var(--border);
  width: 100%;
  max-width: 500px;
  margin: 0 auto;
}

.book-selector-container {
  display: flex;
  align-items: center;
  gap: 1rem;
  width: 100%;
}

.file-label {
  display: flex;
  align-items: center;
  justify-content: center;
  gap: 0.5rem;
  padding: 0.625rem 1.25rem;
  border: 1px solid var(--border);
  background: transparent;
  color: var(--text);
  font-family: inherit;
  font-size: 0.875rem;
  cursor: pointer;
  transition: all var(--transition-speed);
  user-select: none;
  white-space: nowrap;
  flex-shrink: 0;
}

.file-label:hover {
  border-color: var(--text);
}

.file-label input[type="file"] {
  display: none;
}

.file-icon {
  font-size: 1rem;
}

.book-title {
  color: var(--text-muted);
  font-size: 0.875rem;
  flex: 1;
  overflow: hidden;
  text-overflow: ellipsis;
  white-space: nowrap;
  text-align: left;
}

.chapter-selector-container {
  width: 100%;
}

.chapter-select {
  width: 100%;
  padding: 0.625rem 1rem;
  border: 1px solid var(--border);
  background: var(--bg);
  color: var(--text);
  font-family: inherit;
  font-size: 0.875rem;
  cursor: pointer;
  transition: all var(--transition-speed);
  appearance: none;
  -webkit-appearance: none;
  background-image: url("data:image/svg+xml,%3Csvg xmlns='http://www.w3.org/2000/svg' width='12' height='12' viewBox='0 0 12 12'%3E%3Cpath fill='%2371717a' d='M6 8L1 3h10z'/%3E%3C/svg%3E");
  background-repeat: no-repeat;
  background-position: right 1rem center;
  padding-right: 2.5rem;
}

.chapter-select:hover:not(:disabled) {
  border-color: var(--text);
}

.chapter-select:focus {
  outline: 2px solid var(--accent);
  outline-offset: 2px;
}

.chapter-select:disabled {
  opacity: 0.5;
  cursor: not-allowed;
}

.chapter-select option {
  background: var(--bg);
  color: var(--text);
}

.visually-hidden {
  position: absolute;
  width: 1px;
  height: 1px;
  padding: 0;
  margin: -1px;
  overflow: hidden;
  clip: rect(0, 0, 0, 0);
  white-space: nowrap;
  border: 0;
}

/* Disabled button state */
.playback-btn:disabled {
  opacity: 0.5;
  cursor: not-allowed;
}

.playback-btn:disabled:hover {
  border-color: var(--border);
}

/* ================================
   Footer Hints
   ================================ */
.hint-separator {
  margin: 0 0.5rem;
}

/* ================================
   Toast Notifications
   ================================ */
.toast {
  position: fixed;
  bottom: 2rem;
  left: 50%;
  transform: translateX(-50%) translateY(100%);
  padding: 0.75rem 1.5rem;
  background: var(--text);
  color: var(--bg);
  font-family: inherit;
  font-size: 0.875rem;
  border-radius: 4px;
  opacity: 0;
  visibility: hidden;
  transition: all var(--transition-speed);
  z-index: 1000;
}

.toast.visible {
  transform: translateX(-50%) translateY(0);
  opacity: 1;
  visibility: visible;
}

/* ================================
   Selection
   ================================ */
::selection {
  background: var(--text);
  color: var(--bg);
}

/* ================================
   Responsive
   ================================ */
@media (max-width: 768px) {
  .word-display {
    font-size: 3rem;
  }

  .header {
    padding: 1rem;
  }

  .controls-section {
    padding: 1.5rem 1rem;
  }
}

@media (max-width: 480px) {
  .word-display {
    font-size: 2.5rem;
  }

  .speed-presets {
    flex-wrap: wrap;
    justify-content: center;
  }

  .footer {
    font-size: 0.75rem;
  }

  .hint-separator {
    display: none;
  }

  .footer {
    display: flex;
    flex-direction: column;
    gap: 0.25rem;
  }
}

/* ================================
   Accessibility
   ================================ */
@media (prefers-reduced-motion: reduce) {
  *, *::before, *::after {
    animation-duration: 0.01ms !important;
    transition-duration: 0.01ms !important;
  }
}