/* ─── Design tokens ──────────────────────────────────────────────────────────── */

:root {
  --color-bg:       #f8f9fb;
  --color-surface:  #ffffff;
  --color-navy:     #0f172a;
  --color-body:     #1e293b;
  --color-muted:    #64748b;
  --color-border:   #e2e8f0;
  --color-correct:  #0d9488;   /* teal-600  */
  --color-correct-bg: #f0fdfa; /* teal-50   */
  --color-wrong:    #e11d48;   /* rose-600  */
  --color-wrong-bg: #fff1f2;   /* rose-50   */
  --color-amber:    #d97706;   /* amber-600 */
  --color-primary:  #0ea5e9;   /* sky-500   */
  --color-primary-hover: #0284c7;

  --radius-sm: 8px;
  --radius-md: 14px;
  --radius-lg: 20px;

  --shadow-sm: 0 1px 3px rgba(0,0,0,0.08), 0 1px 2px rgba(0,0,0,0.06);
  --shadow-md: 0 4px 12px rgba(0,0,0,0.08), 0 2px 6px rgba(0,0,0,0.05);
}

/* ─── Reset ──────────────────────────────────────────────────────────────────── */

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

/* ─── Base ───────────────────────────────────────────────────────────────────── */

html {
  font-size: 16px;
  -webkit-text-size-adjust: 100%;
}

body {
  font-family: 'DM Sans', system-ui, sans-serif;
  font-size: 1rem;
  line-height: 1.6;
  background: var(--color-bg);
  color: var(--color-body);
  min-height: 100dvh;
}

/* ─── App shell ──────────────────────────────────────────────────────────────── */

.app {
  display: flex;
  flex-direction: column;
  min-height: 100dvh;
  max-width: 480px;
  margin: 0 auto;
  padding: 0 1rem;
}

/* ─── Header ─────────────────────────────────────────────────────────────────── */

.site-header {
  display: flex;
  align-items: center;
  justify-content: flex-end;
  padding: 1rem 0 0.5rem;
}

.nav-link--right {
  margin-left: auto;
}

.site-title {
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: 0.25rem;
  font-size: 0.9rem;
  font-weight: 600;
  letter-spacing: 0.08em;
  text-transform: lowercase;
  color: var(--color-navy);
}

/* ─── Hero ───────────────────────────────────────────────────────────────────── */

.hero {
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: 0.5rem;
  padding: 0.5rem 0 1.5rem;
}

.logo-sun {
  width: 140px;
  height: 140px;
  object-fit: contain;
}

.hero-title {
  font-size: 1.6rem;
  font-weight: 700;
  letter-spacing: 0.06em;
  text-transform: lowercase;
  color: var(--color-navy);
}

/* ─── Byline ─────────────────────────────────────────────────────────────────── */

.byline {
  text-align: center;
  margin-top: 1.5rem;
  padding-bottom: 1rem;
  font-size: 0.8rem;
  color: var(--color-muted);
  letter-spacing: 0.03em;
}

.byline strong {
  color: var(--color-navy);
  font-weight: 600;
}

.view-count {
  text-align: center;
  font-size: 0.75rem;
  color: var(--color-muted);
  margin-top: 0.25rem;
  min-height: 1em;
}

.nav-links {
  display: flex;
  gap: 0.25rem;
}

.nav-link {
  font-size: 0.875rem;
  font-weight: 500;
  color: var(--color-muted);
  text-decoration: none;
  padding: 0.25rem 0.5rem;
  border-radius: var(--radius-sm);
  transition: color 0.15s, background 0.15s;
}

.nav-link:hover {
  color: var(--color-primary);
  background: rgba(14, 165, 233, 0.08);
}

/* ─── About page ─────────────────────────────────────────────────────────────── */

.about-main {
  display: flex;
  flex-direction: column;
  gap: 1rem;
  padding-bottom: 3rem;
}

.about-heading {
  font-size: 1.25rem;
  font-weight: 700;
  color: var(--color-navy);
  letter-spacing: -0.01em;
}

.about-body {
  font-size: 1rem;
  color: var(--color-body);
  line-height: 1.75;
}

/* ─── Screens (quiz page) ────────────────────────────────────────────────────── */

.screen {
  display: none;
  flex-direction: column;
  align-items: center;
  flex: 1;
  animation: fadeIn 0.2s ease;
}

.screen.active {
  display: flex;
}

@keyframes fadeIn {
  from { opacity: 0; transform: translateY(6px); }
  to   { opacity: 1; transform: translateY(0); }
}

/* ─── Question card ──────────────────────────────────────────────────────────── */

.question-card {
  background: var(--color-surface);
  border: 1px solid var(--color-border);
  border-radius: var(--radius-lg);
  padding: 2.5rem 2rem;
  text-align: center;
  width: 100%;
  margin-bottom: 2rem;
  box-shadow: var(--shadow-sm);
}

.question-label {
  font-size: 0.875rem;
  font-weight: 500;
  color: var(--color-muted);
  letter-spacing: 0.02em;
  margin-bottom: 1.25rem;
}

.temp-display {
  display: flex;
  align-items: flex-start;
  justify-content: center;
  gap: 0.2rem;
  line-height: 1;
}

.temp-number {
  font-size: clamp(4rem, 18vw, 6.5rem);
  font-weight: 700;
  color: var(--color-navy);
  letter-spacing: -0.03em;
  line-height: 1;
}

.temp-unit {
  font-size: clamp(1.5rem, 6vw, 2.5rem);
  font-weight: 600;
  color: var(--color-navy);
  margin-top: 0.4rem;
}

.temp-word {
  font-size: 0.875rem;
  font-weight: 400;
  color: var(--color-muted);
  letter-spacing: 0.06em;
  text-transform: uppercase;
  margin-top: 0.75rem;
}

/* ─── Answer form ────────────────────────────────────────────────────────────── */

.answer-form {
  width: 100%;
  display: flex;
  flex-direction: column;
  gap: 0.75rem;
}

.answer-label {
  font-size: 0.875rem;
  font-weight: 500;
  color: var(--color-muted);
  text-align: center;
}

.answer-form input[type="number"] {
  width: 100%;
  min-height: 56px;
  padding: 0.75rem 1rem;
  font-family: inherit;
  font-size: 1.5rem;
  font-weight: 600;
  text-align: center;
  color: var(--color-navy);
  background: var(--color-surface);
  border: 2px solid var(--color-border);
  border-radius: var(--radius-md);
  outline: none;
  transition: border-color 0.15s, box-shadow 0.15s;
  -moz-appearance: textfield;
  appearance: textfield;
}

.answer-form input[type="number"]::-webkit-inner-spin-button,
.answer-form input[type="number"]::-webkit-outer-spin-button {
  -webkit-appearance: none;
}

.answer-form input[type="number"]:focus {
  border-color: var(--color-primary);
  box-shadow: 0 0 0 3px rgba(14, 165, 233, 0.18);
}

.input-error {
  font-size: 0.875rem;
  color: var(--color-wrong);
  text-align: center;
  min-height: 1.2em;
}

/* ─── Buttons ────────────────────────────────────────────────────────────────── */

.btn {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  padding: 0.875rem 1.5rem;
  font-family: inherit;
  font-size: 1rem;
  font-weight: 600;
  border: none;
  border-radius: var(--radius-md);
  cursor: pointer;
  transition: background 0.15s, transform 0.1s, opacity 0.15s;
  min-height: 52px;
  width: 100%;
  letter-spacing: 0.01em;
}

.btn-primary {
  background: var(--color-navy);
  color: #ffffff;
}

.btn-primary:hover {
  background: #1e293b;
}

.btn-primary:active {
  transform: scale(0.98);
}

.btn-primary:disabled {
  opacity: 0.5;
  cursor: not-allowed;
}

.btn-secondary {
  background: transparent;
  color: var(--color-primary);
  border: 2px solid var(--color-primary);
}

.btn-secondary:hover {
  background: rgba(14, 165, 233, 0.06);
}

/* ─── Result screen ──────────────────────────────────────────────────────────── */

.result-badge {
  display: flex;
  align-items: center;
  gap: 0.75rem;
  padding: 1.25rem 2rem;
  border-radius: var(--radius-lg);
  width: 100%;
  margin-bottom: 1.5rem;
  box-shadow: var(--shadow-sm);
}

.result-badge.correct {
  background: var(--color-correct-bg);
  border: 1.5px solid rgba(13, 148, 136, 0.3);
}

.result-badge.wrong {
  background: var(--color-wrong-bg);
  border: 1.5px solid rgba(225, 29, 72, 0.3);
}

.result-icon {
  font-size: 1.75rem;
  font-weight: 700;
  line-height: 1;
}

.result-badge.correct .result-icon { color: var(--color-correct); }
.result-badge.wrong   .result-icon { color: var(--color-wrong); }

.result-text {
  font-size: 1.25rem;
  font-weight: 700;
}

.result-badge.correct .result-text { color: var(--color-correct); }
.result-badge.wrong   .result-text { color: var(--color-wrong); }

.result-details {
  background: var(--color-surface);
  border: 1px solid var(--color-border);
  border-radius: var(--radius-md);
  padding: 1.25rem 1.5rem;
  width: 100%;
  margin-bottom: 1rem;
  display: flex;
  flex-direction: column;
  gap: 0.5rem;
  box-shadow: var(--shadow-sm);
}

.result-equation {
  font-size: 1.375rem;
  font-weight: 700;
  color: var(--color-navy);
  letter-spacing: -0.01em;
}

.result-diff {
  font-size: 0.9375rem;
  color: var(--color-wrong);
  font-weight: 500;
}

.result-diff.hidden { display: none; }

.result-formula {
  font-size: 0.875rem;
  color: var(--color-muted);
  font-variant-numeric: tabular-nums;
}

/* ─── Context note ───────────────────────────────────────────────────────────── */

.result-context {
  display: flex;
  align-items: flex-start;
  gap: 0.5rem;
  background: #fefce8;
  border: 1.5px solid #fde68a;
  border-radius: var(--radius-md);
  padding: 0.875rem 1.25rem;
  width: 100%;
  margin-bottom: 1.5rem;
  font-size: 0.9375rem;
  color: #92400e;
}

.result-context.hidden { display: none; }

.context-label {
  font-weight: 600;
  white-space: nowrap;
}

.context-label::after { content: ': '; }

/* ─── Stats page ─────────────────────────────────────────────────────────────── */

.stats-app .stats-main {
  display: flex;
  flex-direction: column;
  gap: 2rem;
  padding-bottom: 3rem;
}

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

.summary-card {
  background: var(--color-surface);
  border: 1px solid var(--color-border);
  border-radius: var(--radius-md);
  padding: 1rem 0.75rem;
  text-align: center;
  box-shadow: var(--shadow-sm);
}

.summary-value {
  display: block;
  font-size: 1.5rem;
  font-weight: 700;
  color: var(--color-navy);
  letter-spacing: -0.02em;
  line-height: 1.2;
}

.summary-label {
  display: block;
  font-size: 0.75rem;
  color: var(--color-muted);
  margin-top: 0.25rem;
  font-weight: 500;
  text-transform: uppercase;
  letter-spacing: 0.04em;
}

.stats-section {
  background: var(--color-surface);
  border: 1px solid var(--color-border);
  border-radius: var(--radius-lg);
  padding: 1.5rem;
  box-shadow: var(--shadow-sm);
}

.stats-heading {
  font-size: 1rem;
  font-weight: 600;
  color: var(--color-navy);
  margin-bottom: 1.25rem;
  letter-spacing: -0.01em;
}

.chart-wrap {
  position: relative;
}

.chart-empty {
  text-align: center;
  color: var(--color-muted);
  padding: 2rem;
  font-size: 0.9375rem;
}

/* ─── Breakdown table ────────────────────────────────────────────────────────── */

.table-wrap {
  overflow-x: auto;
  -webkit-overflow-scrolling: touch;
}

.breakdown-table {
  width: 100%;
  border-collapse: collapse;
  font-size: 0.9375rem;
}

.breakdown-table th {
  text-align: left;
  padding: 0.5rem 0.75rem;
  font-size: 0.75rem;
  font-weight: 600;
  color: var(--color-muted);
  text-transform: uppercase;
  letter-spacing: 0.05em;
  border-bottom: 2px solid var(--color-border);
}

.breakdown-table td {
  padding: 0.625rem 0.75rem;
  border-bottom: 1px solid var(--color-border);
  font-variant-numeric: tabular-nums;
}

.row-even { background: var(--color-bg); }
.row-odd  { background: var(--color-surface); }

.breakdown-table tr:last-child td { border-bottom: none; }

.td-celsius {
  font-weight: 600;
  color: var(--color-navy);
}

.td-accuracy {
  font-weight: 700;
  border-radius: 4px;
  padding: 0.25rem 0.75rem;
}

.acc-red   { color: var(--color-wrong);   background: var(--color-wrong-bg); }
.acc-amber { color: var(--color-amber);   background: #fffbeb; }
.acc-green { color: var(--color-correct); background: var(--color-correct-bg); }

/* ─── Error state ────────────────────────────────────────────────────────────── */

.stats-error {
  text-align: center;
  padding: 2rem;
  color: var(--color-muted);
}

.stats-error p { margin-bottom: 1rem; }

/* ─── Utility ────────────────────────────────────────────────────────────────── */

.hidden { display: none !important; }

/* ─── Quiz page: fit to screen, no scroll ───────────────────────────────────── */

body.quiz-page {
  overflow: hidden;
  height: 100dvh;
}

body.quiz-page .app {
  height: 100dvh;
  overflow: hidden;
  justify-content: space-between;
}

body.quiz-page .screen {
  flex: 1;
  min-height: 0;
  justify-content: center;
  overflow: hidden;
}

/* Sun + title shrink with viewport height */
body.quiz-page .logo-sun {
  width: clamp(60px, 14dvh, 140px);
  height: clamp(60px, 14dvh, 140px);
}

body.quiz-page .hero {
  padding: clamp(0.1rem, 1dvh, 0.5rem) 0 clamp(0.25rem, 1.5dvh, 1.5rem);
  gap: clamp(0.1rem, 0.8dvh, 0.5rem);
}

body.quiz-page .hero-title {
  font-size: clamp(0.9rem, 2.5dvh, 1.6rem);
}

/* Question card shrinks */
body.quiz-page .question-card {
  padding: clamp(0.75rem, 2.5dvh, 2.5rem) clamp(0.75rem, 3vw, 2rem);
  margin-bottom: clamp(0.5rem, 1.5dvh, 2rem);
}

body.quiz-page .question-label {
  margin-bottom: clamp(0.5rem, 1dvh, 1.25rem);
}

body.quiz-page .temp-number {
  font-size: clamp(2.5rem, 11dvh, 6.5rem);
}

body.quiz-page .temp-unit {
  font-size: clamp(1rem, 4dvh, 2.5rem);
}

body.quiz-page .temp-word {
  margin-top: clamp(0.25rem, 0.8dvh, 0.75rem);
}

/* Form shrinks */
body.quiz-page .answer-form {
  gap: clamp(0.25rem, 1dvh, 0.75rem);
}

body.quiz-page .answer-form input[type="number"] {
  min-height: clamp(44px, 7dvh, 56px);
  font-size: clamp(1.1rem, 3.5dvh, 1.5rem);
}

body.quiz-page .btn {
  min-height: clamp(44px, 6dvh, 52px);
  padding: clamp(0.5rem, 1.5dvh, 0.875rem) 1.5rem;
}

body.quiz-page .byline {
  margin-top: clamp(0.5rem, 1.5dvh, 1.5rem);
}

/* Result screen shrinks */
body.quiz-page .result-badge {
  padding: clamp(0.75rem, 2dvh, 1.25rem) clamp(1rem, 3vw, 2rem);
  margin-bottom: clamp(0.5rem, 1.5dvh, 1.5rem);
}

body.quiz-page .result-details {
  padding: clamp(0.75rem, 2dvh, 1.25rem) clamp(0.75rem, 3vw, 1.5rem);
  margin-bottom: clamp(0.5rem, 1dvh, 1rem);
  gap: clamp(0.2rem, 0.8dvh, 0.5rem);
}

body.quiz-page .result-equation {
  font-size: clamp(1rem, 3.5dvh, 1.375rem);
}

body.quiz-page .result-context {
  padding: clamp(0.5rem, 1.5dvh, 0.875rem) clamp(0.75rem, 2vw, 1.25rem);
  margin-bottom: clamp(0.5rem, 1.5dvh, 1.5rem);
}

/* ─── Responsive tweaks ──────────────────────────────────────────────────────── */

@media (max-width: 360px) {
  .stats-summary {
    grid-template-columns: 1fr 1fr;
  }

  .summary-card:last-child {
    grid-column: span 2;
  }

  .summary-value {
    font-size: 1.25rem;
  }
}