/* ============================================
   Calculate GPA Online — Design System
   Premium Academic Utility Tool
   ============================================ */

/* ---------- CSS Variables ---------- */
:root {
  /* Primary palette */
  --primary-50: #eef2ff;
  --primary-100: #e0e7ff;
  --primary-200: #c7d2fe;
  --primary-300: #a5b4fc;
  --primary-400: #818cf8;
  --primary-500: #6366f1;
  --primary-600: #4f46e5;
  --primary-700: #4338ca;
  --primary-800: #3730a3;
  --primary-900: #312e81;

  /* Accent */
  --accent-400: #34d399;
  --accent-500: #10b981;
  --accent-600: #059669;

  /* Neutrals */
  --gray-50: #f8fafc;
  --gray-100: #f1f5f9;
  --gray-200: #e2e8f0;
  --gray-300: #cbd5e1;
  --gray-400: #94a3b8;
  --gray-500: #64748b;
  --gray-600: #475569;
  --gray-700: #334155;
  --gray-800: #1e293b;
  --gray-900: #0f172a;
  --gray-950: #020617;

  /* Semantic */
  --success: #10b981;
  --warning: #f59e0b;
  --error: #ef4444;
  --info: #3b82f6;

  /* Surfaces */
  --bg-primary: #0f172a;
  --bg-secondary: #1e293b;
  --bg-tertiary: #334155;
  --bg-card: rgba(30, 41, 59, 0.7);
  --bg-glass: rgba(30, 41, 59, 0.5);

  /* Text */
  --text-primary: #f1f5f9;
  --text-secondary: #94a3b8;
  --text-tertiary: #64748b;
  --text-inverse: #0f172a;

  /* Borders */
  --border-subtle: rgba(148, 163, 184, 0.1);
  --border-default: rgba(148, 163, 184, 0.2);
  --border-strong: rgba(148, 163, 184, 0.3);

  /* Shadows */
  --shadow-sm: 0 1px 2px rgba(0, 0, 0, 0.3);
  --shadow-md: 0 4px 6px -1px rgba(0, 0, 0, 0.3), 0 2px 4px -2px rgba(0, 0, 0, 0.3);
  --shadow-lg: 0 10px 15px -3px rgba(0, 0, 0, 0.4), 0 4px 6px -4px rgba(0, 0, 0, 0.3);
  --shadow-xl: 0 20px 25px -5px rgba(0, 0, 0, 0.4), 0 8px 10px -6px rgba(0, 0, 0, 0.3);
  --shadow-glow: 0 0 20px rgba(99, 102, 241, 0.3);

  /* Gradients */
  --gradient-primary: linear-gradient(135deg, #6366f1, #8b5cf6);
  --gradient-accent: linear-gradient(135deg, #10b981, #34d399);
  --gradient-hero: linear-gradient(135deg, #0f172a 0%, #1e1b4b 50%, #0f172a 100%);
  --gradient-card: linear-gradient(135deg, rgba(99, 102, 241, 0.05), rgba(139, 92, 246, 0.05));

  /* Spacing */
  --space-xs: 0.25rem;
  --space-sm: 0.5rem;
  --space-md: 1rem;
  --space-lg: 1.5rem;
  --space-xl: 2rem;
  --space-2xl: 3rem;
  --space-3xl: 4rem;
  --space-4xl: 6rem;

  /* Border Radius */
  --radius-sm: 0.375rem;
  --radius-md: 0.5rem;
  --radius-lg: 0.75rem;
  --radius-xl: 1rem;
  --radius-2xl: 1.5rem;
  --radius-full: 9999px;

  /* Typography */
  --font-sans: 'Inter', -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, sans-serif;
  --font-mono: 'JetBrains Mono', 'Fira Code', monospace;

  /* Transitions */
  --transition-fast: 150ms cubic-bezier(0.4, 0, 0.2, 1);
  --transition-base: 250ms cubic-bezier(0.4, 0, 0.2, 1);
  --transition-slow: 350ms cubic-bezier(0.4, 0, 0.2, 1);

  /* Layout */
  --max-width: 1200px;
  --header-height: 64px;
}

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

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

body {
  font-family: var(--font-sans);
  background-color: var(--bg-primary);
  color: var(--text-primary);
  line-height: 1.7;
  -webkit-font-smoothing: antialiased;
  -moz-osx-font-smoothing: grayscale;
  overflow-x: hidden;
}

img {
  max-width: 100%;
  height: auto;
  display: block;
}

a {
  color: var(--primary-400);
  text-decoration: none;
  transition: color var(--transition-fast);
}

a:hover {
  color: var(--primary-300);
  text-decoration: underline;
}

a:focus-visible {
  outline: 2px solid var(--primary-400);
  outline-offset: 2px;
  border-radius: var(--radius-sm);
}

ul, ol {
  list-style: none;
}

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

input, select, textarea {
  font-family: inherit;
  font-size: 1rem;
}

h1, h2, h3, h4, h5, h6 {
  line-height: 1.3;
  font-weight: 700;
  color: var(--text-primary);
}

/* ---------- Focus Styles (A11y) ---------- */
:focus-visible {
  outline: 2px solid var(--primary-400);
  outline-offset: 2px;
}

/* ---------- Layout ---------- */
.container {
  width: 100%;
  max-width: var(--max-width);
  margin: 0 auto;
  padding: 0 var(--space-lg);
}

.section {
  padding: var(--space-4xl) 0;
}

.section--compact {
  padding: var(--space-2xl) 0;
}

/* ---------- Header ---------- */
.header {
  position: sticky;
  top: 0;
  z-index: 1000;
  background: rgba(15, 23, 42, 0.85);
  backdrop-filter: blur(20px);
  -webkit-backdrop-filter: blur(20px);
  border-bottom: 1px solid var(--border-subtle);
  height: var(--header-height);
  transition: background var(--transition-base);
}

.header__inner {
  display: flex;
  align-items: center;
  justify-content: space-between;
  height: 100%;
}

.header__logo {
  display: flex;
  align-items: center;
  gap: var(--space-sm);
  font-size: 1.125rem;
  font-weight: 700;
  color: var(--text-primary);
  text-decoration: none;
}

.header__logo:hover {
  text-decoration: none;
  color: var(--primary-400);
}

.header__logo-icon {
  width: 32px;
  height: 32px;
  background: var(--gradient-primary);
  border-radius: var(--radius-md);
  display: flex;
  align-items: center;
  justify-content: center;
  font-size: 0.875rem;
  color: white;
  font-weight: 800;
}

.header__nav {
  display: flex;
  align-items: center;
  gap: var(--space-xs);
}

.header__link {
  padding: var(--space-sm) var(--space-md);
  border-radius: var(--radius-md);
  color: var(--text-secondary);
  font-size: 0.875rem;
  font-weight: 500;
  transition: all var(--transition-fast);
  white-space: nowrap;
}

.header__link:hover {
  color: var(--text-primary);
  background: var(--bg-tertiary);
  text-decoration: none;
}

.header__link--active {
  color: var(--primary-400);
  background: rgba(99, 102, 241, 0.1);
}

.header__cta {
  padding: var(--space-sm) var(--space-lg);
  background: var(--gradient-primary);
  color: white;
  border-radius: var(--radius-full);
  font-size: 0.875rem;
  font-weight: 600;
  transition: all var(--transition-fast);
}

.header__cta:hover {
  opacity: 0.9;
  transform: translateY(-1px);
  text-decoration: none;
  color: white;
}

/* Mobile menu toggle */
.header__menu-btn {
  display: none;
  width: 40px;
  height: 40px;
  align-items: center;
  justify-content: center;
  border-radius: var(--radius-md);
  color: var(--text-secondary);
  transition: all var(--transition-fast);
}

.header__menu-btn:hover {
  background: var(--bg-tertiary);
  color: var(--text-primary);
}

.header__menu-btn svg {
  width: 24px;
  height: 24px;
}

@media (max-width: 768px) {
  .header__menu-btn {
    display: flex;
  }

  .header__nav {
    display: none;
    position: absolute;
    top: var(--header-height);
    left: 0;
    right: 0;
    background: rgba(15, 23, 42, 0.98);
    backdrop-filter: blur(20px);
    flex-direction: column;
    padding: var(--space-md);
    border-bottom: 1px solid var(--border-subtle);
    gap: var(--space-xs);
  }

  .header__nav--open {
    display: flex;
  }

  .header__link {
    width: 100%;
    padding: var(--space-md);
  }
}

/* ---------- Hero ---------- */
.hero {
  background: var(--gradient-hero);
  padding: var(--space-3xl) 0 var(--space-xl);
  text-align: center;
  position: relative;
  overflow: hidden;
}

.hero::before {
  content: '';
  position: absolute;
  top: -50%;
  left: -50%;
  width: 200%;
  height: 200%;
  background: radial-gradient(circle at 30% 50%, rgba(99, 102, 241, 0.08), transparent 50%),
              radial-gradient(circle at 70% 50%, rgba(139, 92, 246, 0.06), transparent 50%);
  animation: heroGlow 15s ease-in-out infinite alternate;
}

@keyframes heroGlow {
  0% { transform: translate(0, 0); }
  100% { transform: translate(2%, 1%); }
}

.hero__content {
  position: relative;
  z-index: 1;
}

.hero__badge {
  display: inline-flex;
  align-items: center;
  gap: var(--space-sm);
  padding: var(--space-xs) var(--space-md);
  background: rgba(99, 102, 241, 0.15);
  border: 1px solid rgba(99, 102, 241, 0.3);
  border-radius: var(--radius-full);
  font-size: 0.8125rem;
  color: var(--primary-300);
  font-weight: 500;
  margin-bottom: var(--space-lg);
}

.hero__badge-dot {
  width: 6px;
  height: 6px;
  background: var(--accent-400);
  border-radius: 50%;
  animation: pulse 2s infinite;
}

@keyframes pulse {
  0%, 100% { opacity: 1; }
  50% { opacity: 0.4; }
}

.hero h1 {
  font-size: clamp(2rem, 5vw, 3.25rem);
  font-weight: 800;
  letter-spacing: -0.03em;
  margin-bottom: var(--space-md);
  background: linear-gradient(135deg, #f1f5f9, #c7d2fe);
  -webkit-background-clip: text;
  -webkit-text-fill-color: transparent;
  background-clip: text;
}

.hero__subtitle {
  font-size: clamp(1rem, 2vw, 1.25rem);
  color: var(--text-secondary);
  max-width: 600px;
  margin: 0 auto var(--space-xl);
}

/* ---------- Calculator ---------- */
.calculator {
  background: var(--bg-card);
  border: 1px solid var(--border-default);
  border-radius: var(--radius-2xl);
  backdrop-filter: blur(10px);
  overflow: hidden;
  box-shadow: var(--shadow-xl), var(--shadow-glow);
}

.calculator__header {
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: var(--space-lg) var(--space-xl);
  border-bottom: 1px solid var(--border-subtle);
  background: rgba(99, 102, 241, 0.05);
}

.calculator__title {
  font-size: 1.125rem;
  font-weight: 700;
  display: flex;
  align-items: center;
  gap: var(--space-sm);
}

.calculator__title-icon {
  width: 28px;
  height: 28px;
  background: var(--gradient-primary);
  border-radius: var(--radius-md);
  display: flex;
  align-items: center;
  justify-content: center;
  font-size: 0.875rem;
}

.calculator__scale-select {
  padding: var(--space-sm) var(--space-md);
  background: var(--bg-tertiary);
  border: 1px solid var(--border-default);
  border-radius: var(--radius-md);
  color: var(--text-primary);
  font-size: 0.875rem;
  font-weight: 500;
  cursor: pointer;
  transition: all var(--transition-fast);
}

.calculator__scale-select:hover {
  border-color: var(--primary-400);
}

.calculator__body {
  padding: var(--space-xl);
}

/* Course rows */
.course-list {
  display: flex;
  flex-direction: column;
  gap: var(--space-md);
  margin-bottom: var(--space-lg);
}

.course-row {
  display: grid;
  grid-template-columns: 2fr 1fr 1fr auto;
  gap: var(--space-md);
  align-items: end;
  padding: var(--space-md);
  background: rgba(15, 23, 42, 0.5);
  border: 1px solid var(--border-subtle);
  border-radius: var(--radius-lg);
  transition: all var(--transition-fast);
  animation: slideIn 0.3s ease;
}

@keyframes slideIn {
  from {
    opacity: 0;
    transform: translateY(-10px);
  }
  to {
    opacity: 1;
    transform: translateY(0);
  }
}

.course-row:hover {
  border-color: var(--border-default);
}

.course-row__header {
  display: none;
}

.course-labels {
  display: grid;
  grid-template-columns: 2fr 1fr 1fr auto;
  gap: var(--space-md);
  padding: 0 var(--space-md);
  margin-bottom: var(--space-sm);
}

.course-labels span {
  font-size: 0.75rem;
  font-weight: 600;
  text-transform: uppercase;
  letter-spacing: 0.05em;
  color: var(--text-tertiary);
}

@media (max-width: 600px) {
  .course-labels {
    display: none;
  }

  .course-row {
    grid-template-columns: 1fr 1fr;
    gap: var(--space-sm);
  }

  .course-row .form-field:first-child {
    grid-column: 1 / -1;
  }

  .course-row .btn--icon {
    grid-column: 1 / -1;
    justify-self: end;
  }
}

/* Form fields */
.form-field {
  display: flex;
  flex-direction: column;
  gap: var(--space-xs);
}

.form-field label {
  font-size: 0.75rem;
  font-weight: 600;
  text-transform: uppercase;
  letter-spacing: 0.05em;
  color: var(--text-tertiary);
  display: none;
}

@media (max-width: 600px) {
  .form-field label {
    display: block;
  }
}

.form-input,
.form-select {
  width: 100%;
  padding: var(--space-sm) var(--space-md);
  background: var(--bg-secondary);
  border: 1px solid var(--border-default);
  border-radius: var(--radius-md);
  color: var(--text-primary);
  font-size: 0.9375rem;
  transition: all var(--transition-fast);
}

.form-input::placeholder {
  color: var(--text-tertiary);
}

.form-input:focus,
.form-select:focus {
  outline: none;
  border-color: var(--primary-400);
  box-shadow: 0 0 0 3px rgba(99, 102, 241, 0.15);
}

.form-input:invalid:not(:placeholder-shown) {
  border-color: var(--error);
}

.form-select {
  cursor: pointer;
  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='%2394a3b8' d='M6 8L1 3h10z'/%3E%3C/svg%3E");
  background-repeat: no-repeat;
  background-position: right 12px center;
  padding-right: 32px;
}

/* Buttons */
.btn {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  gap: var(--space-sm);
  padding: var(--space-sm) var(--space-lg);
  border-radius: var(--radius-md);
  font-size: 0.9375rem;
  font-weight: 600;
  transition: all var(--transition-fast);
  white-space: nowrap;
}

.btn--primary {
  background: var(--gradient-primary);
  color: white;
  padding: var(--space-md) var(--space-xl);
  border-radius: var(--radius-lg);
  font-size: 1rem;
  box-shadow: 0 4px 15px rgba(99, 102, 241, 0.3);
}

.btn--primary:hover {
  transform: translateY(-2px);
  box-shadow: 0 6px 20px rgba(99, 102, 241, 0.4);
}

.btn--primary:active {
  transform: translateY(0);
}

.btn--secondary {
  background: var(--bg-tertiary);
  color: var(--text-primary);
  border: 1px solid var(--border-default);
}

.btn--secondary:hover {
  background: var(--bg-secondary);
  border-color: var(--border-strong);
}

.btn--accent {
  background: var(--gradient-accent);
  color: var(--text-inverse);
  padding: var(--space-md) var(--space-xl);
  border-radius: var(--radius-lg);
  font-size: 1rem;
}

.btn--accent:hover {
  transform: translateY(-2px);
  box-shadow: 0 6px 20px rgba(16, 185, 129, 0.3);
}

.btn--ghost {
  color: var(--text-secondary);
  padding: var(--space-sm) var(--space-md);
}

.btn--ghost:hover {
  background: rgba(148, 163, 184, 0.1);
  color: var(--text-primary);
}

.btn--icon {
  width: 36px;
  height: 36px;
  padding: 0;
  border-radius: var(--radius-md);
  color: var(--text-tertiary);
  transition: all var(--transition-fast);
}

.btn--icon:hover {
  background: rgba(239, 68, 68, 0.15);
  color: var(--error);
}

.btn--sm {
  padding: var(--space-xs) var(--space-md);
  font-size: 0.8125rem;
}

.calculator__actions {
  display: flex;
  flex-wrap: wrap;
  gap: var(--space-md);
  align-items: center;
}

.calculator__actions-left {
  display: flex;
  gap: var(--space-md);
}

.calculator__actions-right {
  margin-left: auto;
  display: flex;
  gap: var(--space-sm);
}

/* Result */
.result {
  margin-top: var(--space-xl);
  padding: var(--space-xl);
  background: linear-gradient(135deg, rgba(99, 102, 241, 0.1), rgba(139, 92, 246, 0.1));
  border: 1px solid rgba(99, 102, 241, 0.25);
  border-radius: var(--radius-xl);
  text-align: center;
  display: none;
  animation: fadeInUp 0.5s ease;
}

.result--visible {
  display: block;
}

@keyframes fadeInUp {
  from {
    opacity: 0;
    transform: translateY(20px);
  }
  to {
    opacity: 1;
    transform: translateY(0);
  }
}

.result__gpa {
  font-size: clamp(2.5rem, 5vw, 4rem);
  font-weight: 800;
  background: linear-gradient(135deg, var(--primary-300), var(--accent-400));
  -webkit-background-clip: text;
  -webkit-text-fill-color: transparent;
  background-clip: text;
  margin-bottom: var(--space-sm);
}

.result__label {
  font-size: 0.875rem;
  color: var(--text-tertiary);
  text-transform: uppercase;
  letter-spacing: 0.08em;
  font-weight: 600;
  margin-bottom: var(--space-lg);
}

.result__details {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(140px, 1fr));
  gap: var(--space-md);
  margin-bottom: var(--space-lg);
}

.result__stat {
  padding: var(--space-md);
  background: rgba(15, 23, 42, 0.4);
  border-radius: var(--radius-lg);
  border: 1px solid var(--border-subtle);
}

.result__stat-value {
  font-size: 1.5rem;
  font-weight: 700;
  color: var(--text-primary);
}

.result__stat-label {
  font-size: 0.75rem;
  color: var(--text-tertiary);
  margin-top: var(--space-xs);
}

.result__actions {
  display: flex;
  justify-content: center;
  gap: var(--space-md);
  flex-wrap: wrap;
}

/* Grade Breakdown */
.grade-breakdown {
  margin-top: var(--space-lg);
  padding: var(--space-lg);
  background: rgba(15, 23, 42, 0.4);
  border-radius: var(--radius-lg);
  border: 1px solid var(--border-subtle);
}

.grade-breakdown h4 {
  font-size: 0.875rem;
  text-transform: uppercase;
  letter-spacing: 0.05em;
  color: var(--text-tertiary);
  margin-bottom: var(--space-md);
}

.grade-bar {
  display: flex;
  align-items: center;
  gap: var(--space-md);
  margin-bottom: var(--space-sm);
}

.grade-bar__label {
  width: 30px;
  font-size: 0.875rem;
  font-weight: 600;
  color: var(--text-secondary);
}

.grade-bar__track {
  flex: 1;
  height: 8px;
  background: rgba(15, 23, 42, 0.6);
  border-radius: var(--radius-full);
  overflow: hidden;
}

.grade-bar__fill {
  height: 100%;
  border-radius: var(--radius-full);
  transition: width 0.6s ease;
}

.grade-bar__fill--a { background: var(--accent-400); }
.grade-bar__fill--b { background: var(--primary-400); }
.grade-bar__fill--c { background: var(--warning); }
.grade-bar__fill--d { background: #f97316; }
.grade-bar__fill--f { background: var(--error); }

.grade-bar__count {
  width: 24px;
  font-size: 0.8125rem;
  color: var(--text-tertiary);
  text-align: right;
}

/* ---------- Benefits Row ---------- */
.benefits {
  padding: var(--space-2xl) 0;
  border-bottom: 1px solid var(--border-subtle);
}

.benefits__grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(180px, 1fr));
  gap: var(--space-lg);
}

.benefit {
  display: flex;
  align-items: center;
  gap: var(--space-md);
  padding: var(--space-md) var(--space-lg);
  background: var(--bg-card);
  border: 1px solid var(--border-subtle);
  border-radius: var(--radius-lg);
  transition: all var(--transition-fast);
}

.benefit:hover {
  border-color: var(--primary-500);
  transform: translateY(-2px);
  box-shadow: var(--shadow-md);
}

.benefit__icon {
  width: 40px;
  height: 40px;
  border-radius: var(--radius-md);
  display: flex;
  align-items: center;
  justify-content: center;
  font-size: 1.25rem;
  flex-shrink: 0;
}

.benefit__icon--purple { background: rgba(99, 102, 241, 0.15); }
.benefit__icon--green { background: rgba(16, 185, 129, 0.15); }
.benefit__icon--blue { background: rgba(59, 130, 246, 0.15); }
.benefit__icon--orange { background: rgba(249, 115, 22, 0.15); }
.benefit__icon--pink { background: rgba(236, 72, 153, 0.15); }

.benefit__text {
  font-size: 0.875rem;
  font-weight: 600;
  color: var(--text-primary);
}

/* ---------- Content Sections ---------- */
.content-section {
  padding: var(--space-4xl) 0;
}

.content-section + .content-section {
  border-top: 1px solid var(--border-subtle);
}

.section-header {
  text-align: center;
  margin-bottom: var(--space-2xl);
}

.section-header__tag {
  display: inline-flex;
  align-items: center;
  gap: var(--space-sm);
  padding: var(--space-xs) var(--space-md);
  background: rgba(99, 102, 241, 0.1);
  border: 1px solid rgba(99, 102, 241, 0.2);
  border-radius: var(--radius-full);
  font-size: 0.75rem;
  font-weight: 600;
  text-transform: uppercase;
  letter-spacing: 0.05em;
  color: var(--primary-400);
  margin-bottom: var(--space-md);
}

.section-header h2 {
  font-size: clamp(1.5rem, 3vw, 2.25rem);
  font-weight: 800;
  letter-spacing: -0.02em;
  margin-bottom: var(--space-md);
}

.section-header p {
  font-size: 1.0625rem;
  color: var(--text-secondary);
  max-width: 640px;
  margin: 0 auto;
}

/* Info card */
.info-card {
  background: var(--bg-card);
  border: 1px solid var(--border-subtle);
  border-radius: var(--radius-xl);
  padding: var(--space-xl);
  transition: all var(--transition-base);
}

.info-card:hover {
  border-color: var(--border-default);
  transform: translateY(-2px);
  box-shadow: var(--shadow-lg);
}

.info-card h3 {
  font-size: 1.25rem;
  margin-bottom: var(--space-md);
}

.info-card p {
  color: var(--text-secondary);
  margin-bottom: var(--space-md);
}

.info-card p:last-child {
  margin-bottom: 0;
}

/* Steps */
.steps {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(200px, 1fr));
  gap: var(--space-lg);
  counter-reset: step;
}

.step {
  position: relative;
  padding: var(--space-xl);
  background: var(--bg-card);
  border: 1px solid var(--border-subtle);
  border-radius: var(--radius-xl);
  text-align: center;
  counter-increment: step;
  transition: all var(--transition-base);
}

.step:hover {
  border-color: var(--primary-500);
  transform: translateY(-4px);
  box-shadow: var(--shadow-lg);
}

.step__number {
  width: 48px;
  height: 48px;
  background: var(--gradient-primary);
  border-radius: var(--radius-lg);
  display: flex;
  align-items: center;
  justify-content: center;
  font-size: 1.25rem;
  font-weight: 800;
  color: white;
  margin: 0 auto var(--space-md);
}

.step h3 {
  font-size: 1rem;
  margin-bottom: var(--space-sm);
}

.step p {
  font-size: 0.875rem;
  color: var(--text-secondary);
}

/* Formula block */
.formula-block {
  background: linear-gradient(135deg, rgba(99, 102, 241, 0.08), rgba(139, 92, 246, 0.08));
  border: 1px solid rgba(99, 102, 241, 0.2);
  border-radius: var(--radius-xl);
  padding: var(--space-2xl);
  text-align: center;
  margin: var(--space-xl) 0;
}

.formula {
  font-family: var(--font-mono);
  font-size: clamp(1.125rem, 2.5vw, 1.5rem);
  font-weight: 700;
  color: var(--primary-300);
  padding: var(--space-lg);
  background: rgba(15, 23, 42, 0.5);
  border-radius: var(--radius-lg);
  display: inline-block;
  margin-bottom: var(--space-lg);
}

/* Grade table */
.grade-table {
  width: 100%;
  border-collapse: collapse;
  margin: var(--space-lg) 0;
}

.grade-table th,
.grade-table td {
  padding: var(--space-md) var(--space-lg);
  text-align: left;
  border-bottom: 1px solid var(--border-subtle);
}

.grade-table th {
  font-size: 0.75rem;
  text-transform: uppercase;
  letter-spacing: 0.05em;
  color: var(--text-tertiary);
  font-weight: 700;
  background: rgba(15, 23, 42, 0.5);
}

.grade-table td {
  font-size: 0.9375rem;
  color: var(--text-secondary);
}

.grade-table tr:hover td {
  background: rgba(99, 102, 241, 0.05);
}

.grade-table .grade-letter {
  font-weight: 700;
  color: var(--text-primary);
}

/* Example blocks */
.example-block {
  background: var(--bg-card);
  border: 1px solid var(--border-subtle);
  border-radius: var(--radius-xl);
  overflow: hidden;
  margin-bottom: var(--space-lg);
}

.example-block__header {
  padding: var(--space-md) var(--space-lg);
  background: rgba(99, 102, 241, 0.08);
  border-bottom: 1px solid var(--border-subtle);
  font-weight: 700;
  font-size: 0.9375rem;
  display: flex;
  align-items: center;
  gap: var(--space-sm);
}

.example-block__body {
  padding: var(--space-lg);
}

.example-block__result {
  margin-top: var(--space-md);
  padding: var(--space-md);
  background: rgba(16, 185, 129, 0.1);
  border-radius: var(--radius-lg);
  border: 1px solid rgba(16, 185, 129, 0.2);
  text-align: center;
}

.example-block__result strong {
  font-size: 1.25rem;
  color: var(--accent-400);
}

/* Use cases grid */
.use-cases {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(240px, 1fr));
  gap: var(--space-lg);
}

.use-case {
  display: flex;
  align-items: flex-start;
  gap: var(--space-md);
  padding: var(--space-lg);
  background: var(--bg-card);
  border: 1px solid var(--border-subtle);
  border-radius: var(--radius-xl);
  transition: all var(--transition-base);
}

.use-case:hover {
  border-color: var(--primary-500);
  transform: translateY(-3px);
  box-shadow: var(--shadow-md);
}

.use-case__icon {
  width: 40px;
  height: 40px;
  background: rgba(99, 102, 241, 0.15);
  border-radius: var(--radius-md);
  display: flex;
  align-items: center;
  justify-content: center;
  font-size: 1.125rem;
  flex-shrink: 0;
}

.use-case h3 {
  font-size: 1rem;
  margin-bottom: var(--space-xs);
}

.use-case p {
  font-size: 0.875rem;
  color: var(--text-secondary);
}

/* ---------- FAQ ---------- */
.faq-list {
  max-width: 800px;
  margin: 0 auto;
}

.faq-item {
  border-bottom: 1px solid var(--border-subtle);
}

.faq-item__question {
  width: 100%;
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: var(--space-lg) 0;
  text-align: left;
  font-size: 1rem;
  font-weight: 600;
  color: var(--text-primary);
  cursor: pointer;
  transition: color var(--transition-fast);
  gap: var(--space-md);
  background: transparent;
}

.faq-item__question:hover {
  color: var(--primary-400);
}

.faq-item__icon {
  width: 24px;
  height: 24px;
  display: flex;
  align-items: center;
  justify-content: center;
  border-radius: var(--radius-full);
  background: var(--bg-tertiary);
  flex-shrink: 0;
  transition: all var(--transition-fast);
  font-size: 0.875rem;
  color: var(--text-secondary);
}

.faq-item--open .faq-item__icon {
  background: var(--primary-600);
  color: white;
  transform: rotate(45deg);
}

.faq-item__answer {
  max-height: 0;
  overflow: hidden;
  transition: max-height 0.35s ease, padding 0.35s ease;
}

.faq-item--open .faq-item__answer {
  max-height: 500px;
  padding-bottom: var(--space-lg);
}

.faq-item__answer p {
  color: var(--text-secondary);
  font-size: 0.9375rem;
  line-height: 1.8;
}

/* ---------- Related Calculators ---------- */
.tool-cards {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(280px, 1fr));
  gap: var(--space-lg);
}

.tool-card {
  display: block;
  padding: var(--space-xl);
  background: var(--bg-card);
  border: 1px solid var(--border-subtle);
  border-radius: var(--radius-xl);
  transition: all var(--transition-base);
  text-decoration: none;
}

.tool-card:hover {
  border-color: var(--primary-500);
  transform: translateY(-4px);
  box-shadow: var(--shadow-lg), 0 0 20px rgba(99, 102, 241, 0.1);
  text-decoration: none;
}

.tool-card__icon {
  width: 48px;
  height: 48px;
  border-radius: var(--radius-lg);
  display: flex;
  align-items: center;
  justify-content: center;
  font-size: 1.5rem;
  margin-bottom: var(--space-md);
}

.tool-card__icon--purple { background: rgba(99, 102, 241, 0.15); }
.tool-card__icon--green { background: rgba(16, 185, 129, 0.15); }
.tool-card__icon--blue { background: rgba(59, 130, 246, 0.15); }
.tool-card__icon--orange { background: rgba(249, 115, 22, 0.15); }
.tool-card__icon--pink { background: rgba(236, 72, 153, 0.15); }
.tool-card__icon--cyan { background: rgba(6, 182, 212, 0.15); }

.tool-card h3 {
  font-size: 1.0625rem;
  color: var(--text-primary);
  margin-bottom: var(--space-sm);
}

.tool-card p {
  font-size: 0.875rem;
  color: var(--text-secondary);
  margin-bottom: var(--space-md);
}

.tool-card__link {
  font-size: 0.8125rem;
  font-weight: 600;
  color: var(--primary-400);
  display: flex;
  align-items: center;
  gap: var(--space-xs);
}

/* ---------- Disclaimer Banner ---------- */
.disclaimer-banner {
  padding: var(--space-lg) var(--space-xl);
  background: rgba(249, 115, 22, 0.08);
  border: 1px solid rgba(249, 115, 22, 0.2);
  border-radius: var(--radius-xl);
  display: flex;
  align-items: flex-start;
  gap: var(--space-md);
}

.disclaimer-banner__icon {
  font-size: 1.5rem;
  flex-shrink: 0;
  margin-top: 2px;
}

.disclaimer-banner h4 {
  font-size: 0.9375rem;
  margin-bottom: var(--space-xs);
  color: #f59e0b;
}

.disclaimer-banner p {
  font-size: 0.875rem;
  color: var(--text-secondary);
}

/* ---------- Footer ---------- */
.footer {
  background: rgba(15, 23, 42, 0.8);
  border-top: 1px solid var(--border-subtle);
  padding: var(--space-4xl) 0 var(--space-xl);
}

.footer__grid {
  display: grid;
  grid-template-columns: 2fr 1fr 1fr 1fr;
  gap: var(--space-2xl);
  margin-bottom: var(--space-2xl);
}

@media (max-width: 768px) {
  .footer__grid {
    grid-template-columns: 1fr 1fr;
    gap: var(--space-xl);
  }
}

@media (max-width: 480px) {
  .footer__grid {
    grid-template-columns: 1fr;
  }
}

.footer__brand {
  max-width: 320px;
}

.footer__brand-name {
  display: flex;
  align-items: center;
  gap: var(--space-sm);
  font-size: 1.125rem;
  font-weight: 700;
  color: var(--text-primary);
  margin-bottom: var(--space-md);
}

.footer__brand p {
  font-size: 0.875rem;
  color: var(--text-secondary);
}

.footer__column h4 {
  font-size: 0.75rem;
  text-transform: uppercase;
  letter-spacing: 0.08em;
  color: var(--text-tertiary);
  font-weight: 700;
  margin-bottom: var(--space-lg);
}

.footer__column ul {
  display: flex;
  flex-direction: column;
  gap: var(--space-sm);
}

.footer__column a {
  font-size: 0.875rem;
  color: var(--text-secondary);
  transition: color var(--transition-fast);
}

.footer__column a:hover {
  color: var(--primary-400);
  text-decoration: none;
}

.footer__bottom {
  padding-top: var(--space-xl);
  border-top: 1px solid var(--border-subtle);
  display: flex;
  align-items: center;
  justify-content: space-between;
  flex-wrap: wrap;
  gap: var(--space-md);
}

.footer__copyright {
  font-size: 0.8125rem;
  color: var(--text-tertiary);
}

.footer__bottom-links {
  display: flex;
  gap: var(--space-lg);
}

.footer__bottom-links a {
  font-size: 0.8125rem;
  color: var(--text-tertiary);
}

.footer__bottom-links a:hover {
  color: var(--text-secondary);
}

/* ---------- Breadcrumbs ---------- */
.breadcrumbs {
  padding: var(--space-md) 0;
}

.breadcrumbs__list {
  display: flex;
  align-items: center;
  gap: var(--space-sm);
  flex-wrap: wrap;
}

.breadcrumbs__item {
  font-size: 0.8125rem;
  color: var(--text-tertiary);
}

.breadcrumbs__item a {
  color: var(--text-secondary);
}

.breadcrumbs__item a:hover {
  color: var(--primary-400);
}

.breadcrumbs__separator {
  font-size: 0.75rem;
  color: var(--text-tertiary);
}

/* ---------- Page Content (for inner pages) ---------- */
.page-hero {
  padding: var(--space-3xl) 0 var(--space-xl);
  background: var(--gradient-hero);
  position: relative;
}

.page-hero::before {
  content: '';
  position: absolute;
  inset: 0;
  background: radial-gradient(circle at 30% 50%, rgba(99, 102, 241, 0.06), transparent 50%);
}

.page-hero__content {
  position: relative;
  z-index: 1;
  max-width: 720px;
}

.page-hero h1 {
  font-size: clamp(1.75rem, 4vw, 2.5rem);
  font-weight: 800;
  letter-spacing: -0.02em;
  margin-bottom: var(--space-md);
}

.page-hero p {
  font-size: 1.0625rem;
  color: var(--text-secondary);
}

/* Prose content */
.prose {
  max-width: 800px;
  margin: 0 auto;
}

.prose h2 {
  font-size: 1.5rem;
  margin-top: var(--space-2xl);
  margin-bottom: var(--space-md);
  padding-bottom: var(--space-sm);
  border-bottom: 1px solid var(--border-subtle);
}

.prose h3 {
  font-size: 1.25rem;
  margin-top: var(--space-xl);
  margin-bottom: var(--space-md);
}

.prose p {
  color: var(--text-secondary);
  margin-bottom: var(--space-md);
  font-size: 1rem;
  line-height: 1.8;
}

.prose ul,
.prose ol {
  margin-bottom: var(--space-md);
  padding-left: var(--space-xl);
}

.prose ul {
  list-style: disc;
}

.prose ol {
  list-style: decimal;
}

.prose li {
  color: var(--text-secondary);
  margin-bottom: var(--space-sm);
  font-size: 1rem;
  line-height: 1.7;
}

.prose a {
  color: var(--primary-400);
  text-decoration: underline;
  text-decoration-color: rgba(99, 102, 241, 0.3);
  text-underline-offset: 2px;
}

.prose a:hover {
  text-decoration-color: var(--primary-400);
}

.prose strong {
  color: var(--text-primary);
  font-weight: 600;
}

.prose blockquote {
  border-left: 3px solid var(--primary-500);
  padding-left: var(--space-lg);
  margin: var(--space-lg) 0;
  color: var(--text-secondary);
  font-style: italic;
}

.prose table {
  width: 100%;
  border-collapse: collapse;
  margin: var(--space-lg) 0;
}

.prose table th,
.prose table td {
  padding: var(--space-md);
  text-align: left;
  border-bottom: 1px solid var(--border-subtle);
  font-size: 0.9375rem;
}

.prose table th {
  font-weight: 700;
  color: var(--text-primary);
  background: rgba(15, 23, 42, 0.5);
}

.prose table td {
  color: var(--text-secondary);
}

/* Internal links section */
.internal-links {
  margin-top: var(--space-2xl);
  padding: var(--space-xl);
  background: var(--bg-card);
  border: 1px solid var(--border-subtle);
  border-radius: var(--radius-xl);
}

.internal-links h3 {
  font-size: 1rem;
  margin-bottom: var(--space-md);
}

.internal-links__list {
  display: flex;
  flex-wrap: wrap;
  gap: var(--space-sm);
}

.internal-links__list a {
  display: inline-flex;
  padding: var(--space-sm) var(--space-md);
  background: var(--bg-tertiary);
  border: 1px solid var(--border-subtle);
  border-radius: var(--radius-full);
  font-size: 0.8125rem;
  color: var(--text-secondary);
  transition: all var(--transition-fast);
}

.internal-links__list a:hover {
  border-color: var(--primary-500);
  color: var(--primary-400);
  text-decoration: none;
}

/* ---------- Contact Form ---------- */
.contact-form {
  max-width: 600px;
  margin: 0 auto;
}

.form-group {
  margin-bottom: var(--space-lg);
}

.form-group label {
  display: block;
  font-size: 0.875rem;
  font-weight: 600;
  color: var(--text-primary);
  margin-bottom: var(--space-sm);
}

.form-group .form-input,
.form-group .form-select,
.form-group textarea {
  width: 100%;
  padding: var(--space-md);
  background: var(--bg-secondary);
  border: 1px solid var(--border-default);
  border-radius: var(--radius-lg);
  color: var(--text-primary);
  font-size: 0.9375rem;
  transition: all var(--transition-fast);
}

.form-group textarea {
  min-height: 150px;
  resize: vertical;
  font-family: var(--font-sans);
}

/* ---------- Notification / Toast ---------- */
.toast {
  position: fixed;
  bottom: 24px;
  right: 24px;
  padding: var(--space-md) var(--space-lg);
  background: var(--bg-secondary);
  border: 1px solid var(--border-default);
  border-radius: var(--radius-lg);
  box-shadow: var(--shadow-xl);
  display: flex;
  align-items: center;
  gap: var(--space-md);
  transform: translateY(120%);
  transition: transform 0.3s ease;
  z-index: 10000;
  font-size: 0.875rem;
  color: var(--text-primary);
}

.toast--visible {
  transform: translateY(0);
}

.toast--success {
  border-color: rgba(16, 185, 129, 0.3);
}

/* ---------- Skip to content (A11y) ---------- */
.skip-link {
  position: absolute;
  top: -100px;
  left: var(--space-md);
  padding: var(--space-md) var(--space-lg);
  background: var(--primary-600);
  color: white;
  border-radius: var(--radius-md);
  z-index: 10001;
  font-weight: 600;
  transition: top 0.2s ease;
}

.skip-link:focus {
  top: var(--space-md);
}

/* ---------- Utilities ---------- */
.text-center { text-align: center; }
.text-left { text-align: left; }
.mt-sm { margin-top: var(--space-sm); }
.mt-md { margin-top: var(--space-md); }
.mt-lg { margin-top: var(--space-lg); }
.mt-xl { margin-top: var(--space-xl); }
.mt-2xl { margin-top: var(--space-2xl); }
.mb-md { margin-bottom: var(--space-md); }
.mb-lg { margin-bottom: var(--space-lg); }
.grid-2 { display: grid; grid-template-columns: repeat(2, 1fr); gap: var(--space-lg); }
.grid-3 { display: grid; grid-template-columns: repeat(3, 1fr); gap: var(--space-lg); }

@media (max-width: 768px) {
  .grid-2, .grid-3 {
    grid-template-columns: 1fr;
  }
}

/* ---------- Animations ---------- */
.animate-on-scroll {
  opacity: 0;
  transform: translateY(20px);
  transition: opacity 0.6s ease, transform 0.6s ease;
}

.animate-on-scroll--visible {
  opacity: 1;
  transform: translateY(0);
}

/* Print styles */
@media print {
  .header, .footer, .btn, .header__nav {
    display: none !important;
  }

  body {
    background: white;
    color: black;
  }

  .result {
    border: 2px solid #333;
  }
}

/* ---------- Content Section (Tool Pages) ---------- */
.content-section {
  padding: var(--space-3xl) 0;
  border-top: 1px solid var(--border-subtle);
}

.content-section + .content-section {
  padding-top: var(--space-2xl);
  border-top: none;
}

/* Form Group (Contact, Tool inputs) */
.form-group {
  margin-bottom: var(--space-md);
}

.form-group label {
  display: block;
  font-size: 0.875rem;
  font-weight: 600;
  color: var(--text-primary);
  margin-bottom: var(--space-sm);
}

/* Grade Reference Table */
.grade-table {
  width: 100%;
  border-collapse: collapse;
}

.grade-table th,
.grade-table td {
  padding: var(--space-sm) var(--space-md);
  text-align: left;
  border-bottom: 1px solid var(--border-subtle);
  font-size: 0.9375rem;
}

.grade-table th {
  font-size: 0.75rem;
  font-weight: 700;
  text-transform: uppercase;
  letter-spacing: 0.05em;
  color: var(--text-tertiary);
  background: rgba(15, 23, 42, 0.3);
}

.grade-table tbody tr:hover {
  background: rgba(99, 102, 241, 0.05);
}

/* 5-column responsive for weighted calculator */
@media (max-width: 768px) {
  .course-row[style*="grid-template-columns: 2fr 1fr 1fr 1fr auto"] {
    grid-template-columns: 1fr 1fr !important;
    gap: var(--space-sm);
  }

  .course-row[style*="grid-template-columns: 2fr 1fr 1fr 1fr auto"] .form-field:first-child {
    grid-column: 1 / -1;
  }

  .course-row[style*="grid-template-columns: 2fr 1fr 1fr 1fr auto"] .btn--icon {
    grid-column: 1 / -1;
    justify-self: end;
  }

  .course-labels[style*="grid-template-columns: 2fr 1fr 1fr 1fr auto"] {
    display: none !important;
  }
}

/* Grid 2 column layout */
.grid-2 {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: var(--space-2xl);
  align-items: start;
}

@media (max-width: 768px) {
  .grid-2 {
    grid-template-columns: 1fr;
  }
}

/* Section header for tool pages */
.section-header {
  text-align: center;
  margin-bottom: var(--space-2xl);
}

.section-header h2 {
  font-size: clamp(1.5rem, 3vw, 2rem);
  font-weight: 800;
  margin-bottom: var(--space-sm);
}

.section-header p {
  color: var(--text-secondary);
  max-width: 600px;
  margin: 0 auto;
}

.section-header__tag {
  display: inline-block;
  padding: var(--space-xs) var(--space-md);
  background: rgba(99, 102, 241, 0.1);
  border: 1px solid rgba(99, 102, 241, 0.2);
  border-radius: var(--radius-full);
  font-size: 0.8125rem;
  font-weight: 600;
  color: var(--primary-400);
  margin-bottom: var(--space-md);
}

/* ---------- Language Switcher ---------- */
.lang-switcher {
  position: relative;
  margin-right: var(--space-sm);
}

.lang-switcher__btn {
  display: flex;
  align-items: center;
  gap: var(--space-xs);
  padding: var(--space-xs) var(--space-sm);
  background: var(--bg-tertiary);
  border: 1px solid var(--border-default);
  border-radius: var(--radius-md);
  color: var(--text-secondary);
  font-size: 0.8125rem;
  font-weight: 600;
  cursor: pointer;
  transition: all var(--transition-fast);
  white-space: nowrap;
}

.lang-switcher__btn:hover {
  border-color: var(--primary-400);
  color: var(--text-primary);
}

.lang-switcher__menu {
  display: none;
  position: absolute;
  top: calc(100% + 6px);
  right: 0;
  min-width: 140px;
  background: var(--bg-secondary);
  border: 1px solid var(--border-default);
  border-radius: var(--radius-lg);
  box-shadow: var(--shadow-xl);
  z-index: 1100;
  overflow: hidden;
  animation: fadeInUp 0.2s ease;
}

.lang-switcher:hover .lang-switcher__menu,
.lang-switcher__btn:focus + .lang-switcher__menu,
.lang-switcher__menu:hover {
  display: block;
}

.lang-switcher__menu a {
  display: flex;
  align-items: center;
  gap: var(--space-sm);
  padding: var(--space-sm) var(--space-md);
  color: var(--text-secondary);
  font-size: 0.8125rem;
  font-weight: 500;
  text-decoration: none;
  transition: all var(--transition-fast);
}

.lang-switcher__menu a:hover {
  background: rgba(99, 102, 241, 0.1);
  color: var(--text-primary);
  text-decoration: none;
}

.lang-switcher__menu a.active {
  color: var(--primary-400);
  background: rgba(99, 102, 241, 0.05);
  font-weight: 700;
}

@media (max-width: 768px) {
  .lang-switcher {
    margin: 0;
    width: 100%;
  }

  .lang-switcher__btn {
    width: 100%;
    justify-content: center;
    padding: var(--space-sm) var(--space-md);
  }

  .lang-switcher__menu {
    position: static;
    box-shadow: none;
    border: none;
    background: var(--bg-tertiary);
    border-radius: var(--radius-md);
    margin-top: var(--space-xs);
  }
}