/* ===== Custom properties ===== */
:root {
  --accent:        #2563EB;
  --accent-light:  #EFF6FF;
  --bg:            #F8FAFC;
  --surface:       #FFFFFF;
  --text:          #0F172A;
  --text-muted:    #64748B;
  --border:        #E2E8F0;
  --correct-bg:    #DCFCE7;
  --correct-text:  #166534;
  --correct-border:#16A34A;
  --wrong-bg:      #FEE2E2;
  --wrong-text:    #991B1B;
  --wrong-border:  #DC2626;
  --shadow:        0 1px 3px rgba(0,0,0,.08), 0 1px 2px rgba(0,0,0,.06);
  --radius:        12px;
  --radius-sm:     8px;
}

@media (prefers-color-scheme: dark) {
  :root {
    --bg:            #0F172A;
    --surface:       #1E293B;
    --text:          #F1F5F9;
    --text-muted:    #94A3B8;
    --border:        #334155;
    --accent-light:  #1E3A5F;
    --correct-bg:    #14532D;
    --correct-text:  #86EFAC;
    --correct-border:#16A34A;
    --wrong-bg:      #450A0A;
    --wrong-text:    #FCA5A5;
    --wrong-border:  #DC2626;
    --shadow:        0 1px 3px rgba(0,0,0,.4);
  }
}

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

body {
  font-family: system-ui, -apple-system, BlinkMacSystemFont, 'Segoe UI', sans-serif;
  background: var(--bg);
  color: var(--text);
  font-size: 16px;
  line-height: 1.6;
  -webkit-font-smoothing: antialiased;
}

button {
  font-family: inherit;
  font-size: inherit;
  cursor: pointer;
  border: none;
  background: none;
}

/* ===== Layout ===== */
.quiz-wrap {
  max-width: 640px;
  margin: 0 auto;
  padding: 0 1rem;
}

.screen { display: none; }
.screen.active { display: block; }

/* ===== Language screen ===== */
.lang-screen {
  text-align: center;
  padding: 3rem 0;
}

.lang-screen h2 {
  font-size: 1.25rem;
  font-weight: 600;
  margin-bottom: 0.5rem;
}

.lang-screen p {
  color: var(--text-muted);
  margin-bottom: 2rem;
}

.lang-grid {
  display: flex;
  flex-direction: column;
  gap: 0.75rem;
  max-width: 280px;
  margin: 0 auto;
}

.lang-btn {
  display: flex;
  align-items: center;
  justify-content: center;
  gap: 0.5rem;
  min-height: 52px;
  padding: 0.75rem 1.5rem;
  border: 2px solid var(--border);
  border-radius: var(--radius);
  background: var(--surface);
  color: var(--text);
  font-size: 1rem;
  font-weight: 500;
  box-shadow: var(--shadow);
  transition: border-color .15s, background .15s;
}

.lang-btn:hover {
  border-color: var(--accent);
  background: var(--accent-light);
  color: var(--accent);
}

/* ===== Start screen ===== */
.start-screen {
  text-align: center;
  padding: 2.5rem 0;
}

.start-screen h2 {
  font-size: 1.375rem;
  font-weight: 700;
  margin-bottom: 0.375rem;
}

.start-screen > p {
  color: var(--text-muted);
  margin-bottom: 2rem;
}

.count-grid {
  display: grid;
  grid-template-columns: repeat(5, 1fr);
  gap: 0.625rem;
  margin-bottom: 2rem;
  max-width: 480px;
  margin-left: auto;
  margin-right: auto;
}

@media (max-width: 480px) {
  .count-grid {
    grid-template-columns: repeat(3, 1fr);
    max-width: 320px;
  }
}

.count-btn {
  min-height: 52px;
  padding: 0.75rem 0.5rem;
  border: 2px solid var(--border);
  border-radius: var(--radius-sm);
  background: var(--surface);
  color: var(--text);
  font-size: 1rem;
  font-weight: 600;
  box-shadow: var(--shadow);
  transition: border-color .15s, background .15s, color .15s;
}

.count-btn:hover:not(:disabled) {
  border-color: var(--accent);
  background: var(--accent-light);
  color: var(--accent);
}

.count-btn.selected {
  border-color: var(--accent);
  background: var(--accent-light);
  color: var(--accent);
}

.count-btn:disabled {
  opacity: .35;
  cursor: not-allowed;
}

.start-btn {
  min-height: 52px;
  min-width: 140px;
  padding: 0.75rem 2rem;
  border-radius: var(--radius);
  background: var(--accent);
  color: #fff;
  font-size: 1rem;
  font-weight: 600;
  box-shadow: var(--shadow);
  transition: opacity .15s;
}

.start-btn:disabled {
  opacity: .4;
  cursor: not-allowed;
}

.start-btn:not(:disabled):hover {
  opacity: .9;
}

/* ===== Quiz screen ===== */
.quiz-screen {
  padding: 1.5rem 0 2rem;
}

.progress-bar-bg {
  height: 4px;
  background: var(--border);
  border-radius: 2px;
  margin-bottom: 1.5rem;
  overflow: hidden;
}

.progress-bar-fill {
  height: 4px;
  background: var(--accent);
  border-radius: 2px;
  transition: width 0.3s ease;
}

.question-meta {
  display: flex;
  justify-content: space-between;
  align-items: center;
  font-size: 0.8125rem;
  color: var(--text-muted);
  margin-bottom: 0.75rem;
  font-variant-numeric: tabular-nums;
}

.question-text {
  font-size: 1rem;
  line-height: 1.65;
  font-weight: 500;
  color: var(--text);
  margin-bottom: 1.25rem;
}

/* ===== Answer options ===== */
.options-list {
  display: flex;
  flex-direction: column;
  gap: 0.5rem;
  margin-bottom: 0.25rem;
}

.option-btn {
  display: flex;
  align-items: flex-start;
  gap: 0.625rem;
  width: 100%;
  min-height: 52px;
  padding: 0.75rem 1rem;
  border: 2px solid var(--border);
  border-radius: var(--radius);
  background: var(--surface);
  color: var(--text);
  font-size: 0.9375rem;
  line-height: 1.5;
  text-align: left;
  box-shadow: var(--shadow);
  transition: border-color .15s, background .15s;
}

.option-btn .opt-letter {
  flex-shrink: 0;
  font-weight: 700;
  color: var(--text-muted);
  min-width: 1.25rem;
  transition: color .15s;
}

.option-btn:hover:not(:disabled) {
  border-color: var(--accent);
  background: var(--accent-light);
}

.option-btn:hover:not(:disabled) .opt-letter {
  color: var(--accent);
}

.option-btn.correct {
  border-color: var(--correct-border);
  background: var(--correct-bg);
  color: var(--correct-text);
}

.option-btn.correct .opt-letter { color: var(--correct-text); }

.option-btn.wrong {
  border-color: var(--wrong-border);
  background: var(--wrong-bg);
  color: var(--wrong-text);
}

.option-btn.wrong .opt-letter { color: var(--wrong-text); }

.option-btn:disabled { cursor: default; }

/* ===== Explanation ===== */
.explanation-box {
  margin-top: 1.25rem;
  padding: 1rem 1.125rem;
  border-radius: var(--radius);
  background: var(--surface);
  border: 1px solid var(--border);
  box-shadow: var(--shadow);
}

.explanation-source {
  font-size: 0.75rem;
  color: var(--text-muted);
  margin-bottom: 0.5rem;
  font-weight: 500;
  letter-spacing: .02em;
}

.explanation-label {
  font-size: 0.6875rem;
  font-weight: 700;
  color: var(--text-muted);
  text-transform: uppercase;
  letter-spacing: .07em;
  margin-bottom: 0.625rem;
}

.explanation-box p {
  font-size: 0.875rem;
  line-height: 1.6;
  color: var(--text);
  margin-bottom: 0.5rem;
}

.explanation-box p:last-child { margin-bottom: 0; }

.next-btn {
  display: inline-flex;
  align-items: center;
  margin-top: 1.25rem;
  min-height: 44px;
  padding: 0.625rem 1.5rem;
  border-radius: var(--radius);
  background: var(--accent);
  color: #fff;
  font-size: 0.9375rem;
  font-weight: 600;
  box-shadow: var(--shadow);
  transition: opacity .15s;
}

.next-btn:hover { opacity: .9; }

/* ===== Result screen ===== */
.result-screen {
  text-align: center;
  padding: 2rem 0;
}

.score-circle {
  width: 120px;
  height: 120px;
  border-radius: 50%;
  margin: 0 auto 1.25rem;
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: center;
  font-size: 2rem;
  font-weight: 800;
  line-height: 1;
  box-shadow: var(--shadow);
}

.score-circle span {
  font-size: 0.75rem;
  font-weight: 500;
  margin-top: 0.25rem;
  opacity: .8;
}

.score-pass { background: var(--correct-bg); color: var(--correct-text); }
.score-fail { background: var(--wrong-bg);   color: var(--wrong-text); }

.result-label {
  font-size: 1.375rem;
  font-weight: 700;
  margin-bottom: 0.375rem;
}

.result-sub {
  color: var(--text-muted);
  font-size: 0.9375rem;
  margin-bottom: 2rem;
}

.result-grid {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  gap: 0.75rem;
  max-width: 380px;
  margin: 0 auto 2rem;
}

.result-stat {
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 1rem 0.75rem;
  box-shadow: var(--shadow);
}

.result-stat-val {
  font-size: 1.5rem;
  font-weight: 700;
  line-height: 1.1;
  margin-bottom: 0.25rem;
}

.result-stat-lbl {
  font-size: 0.75rem;
  color: var(--text-muted);
  font-weight: 500;
}

.result-actions {
  display: flex;
  gap: 0.75rem;
  justify-content: center;
  flex-wrap: wrap;
}

.result-actions button {
  min-height: 48px;
  min-width: 44px;
  padding: 0.625rem 1.375rem;
  border-radius: var(--radius);
  font-size: 0.9375rem;
  font-weight: 600;
  box-shadow: var(--shadow);
  transition: opacity .15s;
}

.result-actions button:first-child {
  background: var(--surface);
  border: 2px solid var(--border);
  color: var(--text);
}

.result-actions button:first-child:hover {
  border-color: var(--accent);
  color: var(--accent);
}

#retry-btn {
  background: var(--accent);
  color: #fff;
}

#retry-btn:hover { opacity: .9; }

/* ===== Copyright footer ===== */
.copyright {
  text-align: center;
  font-size: 0.6875rem;
  color: var(--text-muted);
  padding: 1.5rem 1rem 2rem;
  opacity: .6;
}

/* ===== Accessibility ===== */
.sr-only {
  position: absolute;
  width: 1px;
  height: 1px;
  overflow: hidden;
  clip: rect(0,0,0,0);
  white-space: nowrap;
}