/* فونت و متغیرهای پایه */
:root {
  /* Light theme (default) */
  --bg: #f6f8fb;
  --card: #ffffff;
  --text: #1f2937;
  --text-muted: #6b7280;
  --primary: #2563eb;
  --primary-hover: #1d4ed8;
  --primary-light: #eef2ff;
  --error-bg: #fef2f2;
  --error-text: #991b1b;
  --error-border: #fecaca;
  --success-bg: #f0fdf4;
  --success-border: #bbf7d0;
  --success-text: #166534;
  --border: #e5e7eb;
  --border-focus: #2563eb;

  --radius-sm: 8px;
  --radius-md: 12px;
  --radius-lg: 16px;

  --shadow-sm: 0 1px 2px rgba(0,0,0,.05);
  --shadow: 0 1px 3px rgba(0,0,0,.08), 0 1px 2px rgba(0,0,0,.06);
  --shadow-md: 0 4px 12px rgba(0,0,0,.1);
  --shadow-lg: 0 8px 24px rgba(0,0,0,.12), 0 4px 12px rgba(0,0,0,.08);

  --font: 'Vazirmatn', system-ui, -apple-system, sans-serif;

  /* Spacing scale (8px base) */
  --space-1: 4px;
  --space-2: 8px;
  --space-3: 12px;
  --space-4: 16px;
  --space-5: 20px;
  --space-6: 24px;
  --space-8: 32px;
  --space-10: 40px;
  --space-12: 48px;

  /* Touch target minimum */
  --touch-target: 44px;
}

* { box-sizing: border-box; }
html { font-size: 16px; }
body {
  margin: 0;
  font-family: var(--font);
  background: var(--bg);
  color: var(--text);
  line-height: 1.6;
  min-height: 100vh;
  -webkit-font-smoothing: antialiased;
  -moz-osx-font-smoothing: grayscale;
}

/* ==========================================================================
   LAYOUT — Mobile First
   ========================================================================== */

.container {
  width: 100%;
  max-width: 720px;
  margin: 0 auto;
  padding: var(--space-6) var(--space-4) var(--space-10);
}

header {
  text-align: center;
  margin-bottom: var(--space-8);
}
header h1 {
  margin: 0 0 var(--space-2);
  font-size: clamp(1.75rem, 5vw, 2.25rem);
  font-weight: 700;
  color: var(--primary);
  line-height: 1.2;
}
.subtitle {
  margin: 0 0 var(--space-3);
  color: var(--text-muted);
  font-size: clamp(0.9rem, 2.5vw, 1rem);
  line-height: 1.5;
}
.install-btn {
  margin-top: var(--space-3);
  font-size: 0.875rem;
  padding: var(--space-2) var(--space-4);
}

/* ==========================================================================
   CARDS
   ========================================================================== */

.card {
  background: var(--card);
  border-radius: var(--radius-lg);
  box-shadow: var(--shadow);
  border: 1px solid var(--border);
  padding: var(--space-5) var(--space-4);
  margin-bottom: var(--space-5);
  transition: box-shadow 200ms ease, border-color 200ms ease;
}
.card:hover {
  box-shadow: var(--shadow-md);
  border-color: var(--border);
}
.card h2 {
  margin: 0 0 var(--space-5);
  font-size: 1.125rem;
  font-weight: 700;
  color: var(--text);
  border-bottom: 1px solid var(--border);
  padding-bottom: var(--space-3);
  line-height: 1.3;
}

/* ==========================================================================
   FORM ELEMENTS
   ========================================================================== */

label {
  display: block;
  font-size: 0.8125rem;
  font-weight: 500;
  color: var(--text-muted);
  margin-bottom: var(--space-2);
}

input[type="text"] {
  width: 100%;
  min-height: var(--touch-target);
  padding: var(--space-3) var(--space-4);
  border: 1px solid var(--border);
  border-radius: var(--radius-sm);
  font-family: inherit;
  font-size: 1rem;
  text-align: center;
  background: var(--card);
  color: var(--text);
  transition: border-color 150ms ease, box-shadow 150ms ease;
}
input[type="text"]::placeholder {
  color: var(--text-muted);
  opacity: 0.7;
}
input[type="text"]:hover {
  border-color: #d1d5db;
}
input[type="text"]:focus {
  outline: none;
  border-color: var(--border-focus);
  box-shadow: 0 0 0 3px rgba(37, 99, 235, 0.15);
}
input[type="text"]:disabled {
  background: var(--bg);
  color: var(--text-muted);
  cursor: not-allowed;
}

/* ==========================================================================
   FRACTION INPUTS — Stacked on mobile, side-by-side on desktop
   ========================================================================== */

.fraction-inputs-vertical {
  display: flex;
  flex-direction: column;
  gap: var(--space-4);
}

.fraction-group {
  width: 100%;
}
.fraction-group.single {
  max-width: 100%;
}

.fraction-row {
  display: flex;
  align-items: center;
  gap: var(--space-2);
}
.fraction-row input {
  flex: 1;
  min-width: 0; /* allows shrinking */
}
.frac-bar {
  flex-shrink: 0;
  font-size: 1.5rem;
  font-weight: 700;
  color: var(--text-muted);
  user-select: none;
  padding: 0 var(--space-1);
}

/* ==========================================================================
   TWO-INPUT ROW (GCD/LCM)
   ========================================================================== */

.two-inputs {
  display: flex;
  flex-direction: column;
  gap: var(--space-4);
}
.two-inputs .input-group {
  width: 100%;
}

/* ==========================================================================
   BUTTONS
   ========================================================================== */

.ops {
  display: flex;
  flex-wrap: wrap;
  gap: var(--space-3);
  margin-top: var(--space-4);
}

.btn {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  gap: var(--space-2);
  min-height: var(--touch-target);
  padding: var(--space-3) var(--space-5);
  border: none;
  border-radius: var(--radius-sm);
  font-family: inherit;
  font-size: 0.9375rem;
  font-weight: 500;
  cursor: pointer;
  transition: background-color 150ms ease, transform 50ms ease, box-shadow 150ms ease;
  white-space: nowrap;
}
.btn:active { transform: scale(0.98); }
.btn:focus-visible {
  outline: none;
  box-shadow: 0 0 0 3px rgba(37, 99, 235, 0.35);
}

.btn.primary {
  background: var(--primary);
  color: #fff;
}
.btn.primary:hover { background: var(--primary-hover); }
.btn.primary:active { background: #1e40af; }

.btn:not(.primary) {
  background: var(--primary-light);
  color: var(--primary);
  border: 1px solid var(--border);
}
.btn:not(.primary):hover {
  background: #e0e7ff;
  border-color: var(--primary);
}

.btn.ghost {
  background: transparent;
  color: var(--text-muted);
  border: 1px solid var(--border);
}
.btn.ghost:hover {
  background: var(--bg);
  color: var(--text);
  border-color: var(--text-muted);
}
.btn.ghost:focus-visible {
  box-shadow: 0 0 0 3px rgba(107, 114, 128, 0.35);
}

.btn-group {
  display: flex;
  flex-wrap: wrap;
  gap: var(--space-3);
  margin-top: var(--space-4);
  align-items: center;
}

/* Full-width buttons on mobile for primary actions */
@media (max-width: 480px) {
  .btn.primary {
    width: 100%;
  }
  .ops .btn {
    flex: 1 1 calc(50% - var(--space-3)/2);
    min-width: 0;
  }
}

/* ==========================================================================
   RESULTS & STATES
   ========================================================================== */

.result-area {
  margin-top: var(--space-4);
  padding: var(--space-4);
  background: var(--success-bg);
  border: 1px solid var(--success-border);
  border-radius: var(--radius-sm);
  animation: fadeIn 200ms ease;
}
@keyframes fadeIn {
  from { opacity: 0; transform: translateY(-4px); }
  to { opacity: 1; transform: none; }
}
.result-line {
  margin: var(--space-2) 0;
  font-size: 0.9375rem;
  line-height: 1.5;
}
.result-line:first-child { margin-top: 0; }
.result-line:last-child { margin-bottom: 0; }
.result-line strong {
  color: var(--text);
  font-weight: 600;
}
.result-line span {
  font-family: 'SF Mono', 'Fira Code', monospace;
  font-size: 1.0625rem;
  font-weight: 600;
  color: var(--primary);
  word-break: break-all;
}
.result-line.decimal {
  margin-top: var(--space-3);
  padding-top: var(--space-3);
  border-top: 1px solid var(--success-border);
}
.result-line.decimal span {
  color: var(--text);
  font-weight: 500;
}

.hint {
  margin: calc(-1 * var(--space-3)) 0 var(--space-4);
  font-size: 0.8125rem;
  color: var(--text-muted);
  line-height: 1.5;
}

.error {
  margin-top: var(--space-3);
  padding: var(--space-3) var(--space-4);
  background: var(--error-bg);
  border: 1px solid var(--error-border);
  border-radius: var(--radius-sm);
  color: var(--error-text);
  font-size: 0.875rem;
  line-height: 1.5;
  animation: fadeIn 200ms ease;
}

/* ==========================================================================
   FOOTER
   ========================================================================== */

footer {
  text-align: center;
  margin-top: var(--space-8);
  padding-top: var(--space-6);
  border-top: 1px solid var(--border);
  color: var(--text-muted);
  font-size: 0.8125rem;
}

/* ==========================================================================
   RESPONSIVE — Tablet and up
   ========================================================================== */

@media (min-width: 560px) {
  .container {
    padding: var(--space-8) var(--space-6) var(--space-12);
  }

  .card {
    padding: var(--space-6) var(--space-5);
    margin-bottom: var(--space-6);
  }

  .card h2 {
    margin-bottom: var(--space-6);
    font-size: 1.25rem;
  }

  /* Fraction inputs side-by-side on tablet+ */
  .fraction-inputs-vertical {
    flex-direction: row;
    align-items: flex-start;
    gap: var(--space-6);
  }
  .fraction-group {
    flex: 1;
    min-width: 0;
  }
  .fraction-group.single {
    max-width: 360px;
    margin: 0 auto;
  }

  /* Two inputs side-by-side on tablet+ */
  .two-inputs {
    flex-direction: row;
    gap: var(--space-4);
  }
  .two-inputs .input-group {
    flex: 1;
    min-width: 0;
  }

  /* Buttons: don't force full-width on tablet */
  .btn.primary {
    width: auto;
  }
  .ops {
    justify-content: flex-start;
  }
  .ops .btn {
    flex: 0 0 auto;
  }
  .btn-group {
    justify-content: flex-start;
  }
  .btn-group .btn {
    flex: 0 0 auto;
  }
}

@media (min-width: 768px) {
  header {
    margin-bottom: var(--space-10);
  }
  header h1 {
    font-size: 2.25rem;
  }

  .card {
    padding: var(--space-6);
  }

  .fraction-row input {
    padding: var(--space-3) var(--space-4);
    font-size: 1.0625rem;
  }
  .frac-bar {
    font-size: 1.75rem;
  }
}

/* ==========================================================================
   REDUCED MOTION
   ========================================================================== */

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

/* ==========================================================================
   HIGH CONTRAST MODE (for accessibility)
   ========================================================================== */

@media (prefers-contrast: high) {
  :root {
    --border: #000;
    --primary: #0000ee;
    --primary-hover: #0000cc;
    --text-muted: #333;
  }
  .card { border-width: 2px; }
  input[type="text"] { border-width: 2px; }
  .btn:not(.primary) { border-width: 2px; }
  .result-area { border-width: 2px; }
  .error { border-width: 2px; }
}