/* ===========================
   Reset & Base
   =========================== */

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

:root {
  --color-base: #0f172a;
  --color-surface: #1e293b;
  --color-surface-raised: #334155;
  --color-border: rgba(148, 163, 184, 0.12);
  --color-border-hover: rgba(148, 163, 184, 0.25);

  --color-text: #f1f5f9;
  --color-text-secondary: #94a3b8;
  --color-text-muted: #64748b;

  --accent-start: #6366f1;
  --accent-end: #8b5cf6;
  --accent-gradient: linear-gradient(135deg, var(--accent-start), var(--accent-end));

  --color-correct: #10b981;
  --color-correct-soft: rgba(16, 185, 129, 0.15);
  --color-error: #f43f5e;
  --color-error-soft: rgba(244, 63, 94, 0.15);
  --color-warning: #f59e0b;
  --color-warning-soft: rgba(245, 158, 11, 0.15);

  --radius-sm: 0.5rem;
  --radius-md: 0.75rem;
  --radius-lg: 1rem;
  --radius-xl: 1.25rem;
  --radius-full: 9999px;

  --shadow-sm: 0 1px 2px rgba(0, 0, 0, 0.3);
  --shadow-md: 0 4px 12px rgba(0, 0, 0, 0.25);
  --shadow-lg: 0 8px 32px rgba(0, 0, 0, 0.35);

  --transition-fast: 150ms ease;
  --transition-base: 250ms ease;
  --transition-slow: 400ms ease;

  --font-sans: 'Inter', system-ui, -apple-system, sans-serif;
}

html {
  font-size: 16px;
  -webkit-font-smoothing: antialiased;
  -moz-osx-font-smoothing: grayscale;
}

body {
  font-family: var(--font-sans);
  background-color: var(--color-base);
  color: var(--color-text);
  line-height: 1.6;
  min-height: 100vh;
  display: flex;
  align-items: center;
  justify-content: center;
  padding: 1rem;
  background-image:
    radial-gradient(ellipse 80% 60% at 50% -20%, rgba(99, 102, 241, 0.12), transparent),
    radial-gradient(ellipse 60% 50% at 80% 50%, rgba(139, 92, 246, 0.06), transparent);
}

#app {
  width: 100%;
  max-width: 40rem;
}

/* ===========================
   Typography
   =========================== */

h1, h2, h3 {
  font-weight: 700;
  line-height: 1.2;
  letter-spacing: -0.02em;
}

h1 { font-size: 2rem; }
h2 { font-size: 1.5rem; }
h3 { font-size: 1.125rem; }

/* ===========================
   Components: Buttons
   =========================== */

.btn {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  gap: 0.5rem;
  padding: 0.75rem 1.5rem;
  font-family: var(--font-sans);
  font-size: 0.9375rem;
  font-weight: 600;
  line-height: 1;
  border: none;
  border-radius: var(--radius-md);
  cursor: pointer;
  transition:
    background var(--transition-fast),
    transform var(--transition-fast),
    box-shadow var(--transition-fast),
    opacity var(--transition-fast);
  user-select: none;
  -webkit-tap-highlight-color: transparent;
}

.btn:active:not(:disabled) {
  transform: scale(0.97);
}

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

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

.btn-primary {
  background: var(--accent-gradient);
  color: #fff;
  box-shadow: 0 2px 12px rgba(99, 102, 241, 0.3);
}

.btn-primary:hover:not(:disabled) {
  box-shadow: 0 4px 20px rgba(99, 102, 241, 0.45);
  filter: brightness(1.08);
}

.btn-icon {
  font-size: 1.15em;
  transition: transform var(--transition-fast);
}

.btn:hover .btn-icon {
  transform: translateX(3px);
}

.hidden {
  display: none !important;
}

/* ===========================
   Components: Start Screen
   =========================== */

.start-screen {
  display: flex;
  flex-direction: column;
  align-items: center;
  text-align: center;
  gap: 1.25rem;
  background: rgba(30, 41, 59, 0.6);
  backdrop-filter: blur(16px);
  -webkit-backdrop-filter: blur(16px);
  border: 1px solid var(--color-border);
  border-radius: var(--radius-xl);
  padding: 3rem 2rem;
  box-shadow: var(--shadow-lg);
}

.start-emoji {
  font-size: 3.5rem;
  line-height: 1;
  animation: scaleIn var(--transition-slow) ease both;
}

.start-title {
  font-size: 2.25rem;
  background: var(--accent-gradient);
  -webkit-background-clip: text;
  background-clip: text;
  -webkit-text-fill-color: transparent;
}

.start-subtitle {
  color: var(--color-text-secondary);
  font-size: 1rem;
  max-width: 28rem;
  line-height: 1.6;
}

.start-meta {
  display: flex;
  gap: 0.75rem;
  flex-wrap: wrap;
  justify-content: center;
}

.meta-badge {
  display: inline-flex;
  align-items: center;
  gap: 0.375rem;
  padding: 0.375rem 0.875rem;
  font-size: 0.8125rem;
  font-weight: 500;
  border-radius: var(--radius-full);
  background: rgba(148, 163, 184, 0.08);
  color: var(--color-text-muted);
  border: 1px solid var(--color-border);
}

.btn-start {
  margin-top: 0.5rem;
  padding: 1rem 2.5rem;
  font-size: 1rem;
  border-radius: var(--radius-lg);
}

/* Timer Toggle */

.timer-toggle {
  display: inline-flex;
  align-items: center;
  gap: 0.625rem;
  cursor: pointer;
  user-select: none;
  padding: 0.5rem 1rem;
  border-radius: var(--radius-full);
  background: rgba(148, 163, 184, 0.06);
  border: 1px solid var(--color-border);
  transition: border-color var(--transition-fast);
}

.timer-toggle:hover {
  border-color: var(--color-border-hover);
}

.timer-toggle input[type="checkbox"] {
  position: absolute;
  opacity: 0;
  width: 0;
  height: 0;
}

.toggle-slider {
  position: relative;
  width: 2.5rem;
  height: 1.375rem;
  background: var(--color-surface-raised);
  border-radius: var(--radius-full);
  transition: background var(--transition-fast);
  flex-shrink: 0;
}

.toggle-slider::after {
  content: '';
  position: absolute;
  top: 0.1875rem;
  left: 0.1875rem;
  width: 1rem;
  height: 1rem;
  background: var(--color-text-muted);
  border-radius: 50%;
  transition: transform var(--transition-fast), background var(--transition-fast);
}

.timer-toggle input:checked + .toggle-slider {
  background: var(--accent-start);
}

.timer-toggle input:checked + .toggle-slider::after {
  transform: translateX(1.125rem);
  background: #fff;
}

.toggle-label {
  font-size: 0.8125rem;
  font-weight: 500;
  color: var(--color-text-secondary);
}

/* ===========================
   Components: Quiz Screen
   =========================== */

.quiz-screen {
  display: flex;
  flex-direction: column;
  gap: 1.25rem;
}

.quiz-top-bar {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 0.75rem;
}

.quiz-progress-text {
  font-size: 0.8125rem;
  font-weight: 500;
  color: var(--color-text-muted);
}

.quiz-score-badge {
  display: inline-flex;
  align-items: center;
  gap: 0.375rem;
  padding: 0.375rem 0.875rem;
  font-size: 0.8125rem;
  font-weight: 600;
  border-radius: var(--radius-full);
  background: rgba(99, 102, 241, 0.12);
  color: var(--accent-start);
  border: 1px solid rgba(99, 102, 241, 0.2);
}

.quiz-timer {
  font-size: 0.9375rem;
  font-weight: 700;
  font-variant-numeric: tabular-nums;
  color: var(--color-text);
  min-width: 3rem;
  text-align: right;
  transition: color var(--transition-fast);
}

.quiz-timer.warning {
  color: var(--color-warning);
  animation: pulse 1s ease-in-out infinite;
}

.quiz-timer.timeout {
  color: var(--color-error);
  animation: none;
}

/* Progress Bar */

.progress-bar {
  width: 100%;
  height: 0.375rem;
  background: rgba(148, 163, 184, 0.1);
  border-radius: var(--radius-full);
  overflow: hidden;
}

.progress-fill {
  height: 100%;
  background: var(--accent-gradient);
  border-radius: var(--radius-full);
  transition: width var(--transition-base);
}

/* Question Card */

.question-card {
  background: rgba(30, 41, 59, 0.6);
  backdrop-filter: blur(16px);
  -webkit-backdrop-filter: blur(16px);
  border: 1px solid var(--color-border);
  border-radius: var(--radius-xl);
  padding: 2rem;
  box-shadow: var(--shadow-lg);
  display: flex;
  flex-direction: column;
  gap: 1rem;
  animation: fadeIn var(--transition-slow) ease both;
}

.category-badge {
  display: inline-flex;
  align-self: flex-start;
  padding: 0.25rem 0.625rem;
  font-size: 0.6875rem;
  font-weight: 600;
  text-transform: uppercase;
  letter-spacing: 0.06em;
  border-radius: var(--radius-full);
  background: rgba(148, 163, 184, 0.08);
  color: var(--color-text-muted);
  border: 1px solid var(--color-border);
}

.question-text {
  font-size: 1.25rem;
  font-weight: 600;
  line-height: 1.4;
  letter-spacing: -0.01em;
}

/* Answer Buttons */

.answers-grid {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 0.75rem;
}

.answer-btn {
  display: flex;
  align-items: center;
  width: 100%;
  padding: 1rem 1.25rem;
  font-family: var(--font-sans);
  font-size: 0.9375rem;
  font-weight: 500;
  color: var(--color-text);
  text-align: left;
  background: rgba(51, 65, 85, 0.4);
  border: 1px solid var(--color-border);
  border-radius: var(--radius-md);
  cursor: pointer;
  transition:
    background var(--transition-fast),
    border-color var(--transition-fast),
    transform var(--transition-fast),
    box-shadow var(--transition-fast),
    color var(--transition-fast);
  -webkit-tap-highlight-color: transparent;
}

.answer-btn:hover:not(:disabled) {
  background: rgba(51, 65, 85, 0.7);
  border-color: var(--color-border-hover);
  transform: translateY(-1px);
}

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

.answer-btn:disabled {
  cursor: default;
  transform: none;
}

.answer-btn.correct {
  border-color: var(--color-correct);
  background: var(--color-correct-soft);
  box-shadow: 0 0 0 1px var(--color-correct);
  color: var(--color-correct);
}

.answer-btn.incorrect {
  border-color: var(--color-error);
  background: var(--color-error-soft);
  box-shadow: 0 0 0 1px var(--color-error);
  color: var(--color-error);
}

/* Next Button */

.btn-next {
  align-self: flex-end;
  padding: 0.875rem 2rem;
  font-size: 0.9375rem;
  border-radius: var(--radius-lg);
  animation: fadeIn var(--transition-base) ease both;
}

/* ===========================
   Components: Results Screen
   =========================== */

.results-screen {
  display: flex;
  flex-direction: column;
  align-items: center;
  text-align: center;
  gap: 1.5rem;
  background: rgba(30, 41, 59, 0.6);
  backdrop-filter: blur(16px);
  -webkit-backdrop-filter: blur(16px);
  border: 1px solid var(--color-border);
  border-radius: var(--radius-xl);
  padding: 2.5rem 2rem;
  box-shadow: var(--shadow-lg);
}

.score-ring {
  position: relative;
  width: 8rem;
  height: 8rem;
}

.score-svg {
  width: 100%;
  height: 100%;
  transform: rotate(-90deg);
}

.score-bg {
  fill: none;
  stroke: rgba(148, 163, 184, 0.1);
  stroke-width: 6;
}

.score-fill {
  fill: none;
  stroke: var(--accent-start);
  stroke-width: 6;
  stroke-linecap: round;
  transition: stroke-dasharray 1s ease;
}

.score-value {
  position: absolute;
  inset: 0;
  display: flex;
  align-items: center;
  justify-content: center;
  font-size: 1.75rem;
  font-weight: 700;
  letter-spacing: -0.02em;
}

.score-message {
  font-size: 1.125rem;
  font-weight: 500;
  color: var(--color-text-secondary);
}

.raw-score {
  font-size: 0.875rem;
  color: var(--color-text-muted);
  margin-top: -0.5rem;
}

/* Stats Row */

.stats-row {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  gap: 0.75rem;
  width: 100%;
}

.stat-card {
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: 0.25rem;
  padding: 1rem 0.5rem;
  background: rgba(51, 65, 85, 0.3);
  border-radius: var(--radius-md);
  border: 1px solid var(--color-border);
}

.stat-icon {
  font-size: 1.125rem;
  line-height: 1;
}

.stat-count {
  font-size: 1.25rem;
  font-weight: 700;
}

.stat-correct .stat-icon,
.stat-correct .stat-count { color: var(--color-correct); }

.stat-incorrect .stat-icon,
.stat-incorrect .stat-count { color: var(--color-error); }

.stat-timeout .stat-icon,
.stat-timeout .stat-count { color: var(--color-warning); }

.stat-label {
  font-size: 0.75rem;
  color: var(--color-text-muted);
  text-transform: uppercase;
  letter-spacing: 0.05em;
}

/* Summary */

.summary-title {
  align-self: flex-start;
  margin-bottom: -0.5rem;
}

.summary-list {
  width: 100%;
  text-align: left;
}

.summary-row {
  display: flex;
  gap: 0.75rem;
  padding: 1rem 0;
  border-bottom: 1px solid var(--color-border);
  align-items: flex-start;
}

.summary-row:last-child {
  border-bottom: none;
  padding-bottom: 0;
}

.summary-icon {
  flex-shrink: 0;
  width: 1.5rem;
  height: 1.5rem;
  display: flex;
  align-items: center;
  justify-content: center;
  font-size: 0.75rem;
  font-weight: 700;
  border-radius: 50%;
  margin-top: 0.125rem;
}

.row-correct .summary-icon {
  background: var(--color-correct-soft);
  color: var(--color-correct);
}

.row-incorrect .summary-icon {
  background: var(--color-error-soft);
  color: var(--color-error);
}

.summary-details {
  flex: 1;
  min-width: 0;
}

.summary-question {
  font-size: 0.875rem;
  font-weight: 500;
  margin-bottom: 0.375rem;
  line-height: 1.4;
}

.summary-user-answer {
  font-size: 0.8125rem;
  color: var(--color-text-secondary);
}

.summary-correct-answer {
  font-size: 0.8125rem;
  color: var(--color-correct);
  margin-top: 0.125rem;
}

.btn-restart {
  margin-top: 0.5rem;
  padding: 1rem 2.5rem;
  font-size: 1rem;
  border-radius: var(--radius-lg);
}

/* ===========================
   Components: Error Screen
   =========================== */

.error-screen {
  display: flex;
  flex-direction: column;
  align-items: center;
  text-align: center;
  gap: 1rem;
  background: rgba(30, 41, 59, 0.6);
  backdrop-filter: blur(16px);
  -webkit-backdrop-filter: blur(16px);
  border: 1px solid var(--color-border);
  border-radius: var(--radius-xl);
  padding: 3rem 2rem;
  box-shadow: var(--shadow-lg);
}

.error-icon {
  font-size: 3rem;
  line-height: 1;
}

.error-screen h2 {
  color: var(--color-error);
}

.error-screen p {
  color: var(--color-text-secondary);
  max-width: 24rem;
}

/* ===========================
   Animations
   =========================== */

@keyframes fadeIn {
  from {
    opacity: 0;
    transform: translateY(8px);
  }
  to {
    opacity: 1;
    transform: translateY(0);
  }
}

@keyframes scaleIn {
  from {
    opacity: 0;
    transform: scale(0.9);
  }
  to {
    opacity: 1;
    transform: scale(1);
  }
}

@keyframes pulse {
  0%, 100% { opacity: 1; }
  50% { opacity: 0.5; }
}

.fade-in {
  animation: fadeIn var(--transition-slow) ease both;
}

/* ===========================
   Utilities
   =========================== */

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

/* ===========================
   Media Queries
   =========================== */

@media (max-width: 480px) {
  html { font-size: 15px; }

  .start-screen,
  .question-card,
  .results-screen { padding: 1.5rem 1.25rem; }

  h1 { font-size: 1.625rem; }
  h2 { font-size: 1.25rem; }

  .start-title { font-size: 1.875rem; }
  .question-text { font-size: 1.1rem; }

  .answers-grid {
    grid-template-columns: 1fr;
  }

  .stats-row { gap: 0.5rem; }
  .stat-card { padding: 0.75rem 0.25rem; }

  .btn-start,
  .btn-restart {
    padding: 0.875rem 1.5rem;
    font-size: 0.9375rem;
    width: 100%;
  }

  .score-ring {
    width: 6.5rem;
    height: 6.5rem;
  }

  .score-value { font-size: 1.5rem; }
}

@media (min-width: 481px) and (max-width: 768px) {
  .start-screen,
  .question-card,
  .results-screen { padding: 2rem 1.75rem; }
}

@media (min-width: 1024px) {
  .answer-btn:hover:not(:disabled) {
    transform: translateY(-2px);
    box-shadow: var(--shadow-sm);
  }
}

@media (prefers-reduced-motion: reduce) {
  *, *::before, *::after {
    animation-duration: 0.01ms !important;
    animation-iteration-count: 1 !important;
    transition-duration: 0.01ms !important;
  }
}