:root {
  --primary: #3b82f6;
  --primary-dark: #2563eb;
  --primary-light: #dbeafe;
  --secondary: #8b5cf6;
  --success: #10b981;
  --warning: #f59e0b;
  --danger: #ef4444;
  --bg: #f8fafc;
  --bg-dark: #1e293b;
  --card: #ffffff;
  --text-primary: #0f172a;
  --text-muted: #64748b;
  --border: #e2e8f0;
  --shadow-sm: 0 1px 2px rgba(0, 0, 0, 0.05);
  --shadow-md: 0 4px 6px rgba(0, 0, 0, 0.07);
  --shadow-lg: 0 10px 15px rgba(0, 0, 0, 0.1);
  --shadow-xl: 0 20px 25px rgba(0, 0, 0, 0.1);
  --radius: 12px;
  --radius-lg: 16px;
  --max: 1200px;
}

* {
  box-sizing: border-box;
  -webkit-font-smoothing: antialiased;
  -moz-osx-font-smoothing: grayscale;
}

html {
  scroll-behavior: smooth;
}

body {
  font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', 'Roboto', 'Oxygen', 'Ubuntu', 'Cantarell', 'Fira Sans', 'Droid Sans', 'Helvetica Neue', sans-serif;
  margin: 0;
  background: linear-gradient(135deg, var(--bg) 0%, #f0f4f8 100%);
  color: var(--text-primary);
  line-height: 1.6;
  min-height: 100vh;
}

.reveal {
  opacity: 0;
  transform: translateY(16px);
  transition: opacity 0.6s ease, transform 0.6s ease;
}

.reveal.visible {
  opacity: 1;
  transform: translateY(0);
}

/* Hero Section */
.hero {
  background: linear-gradient(135deg, var(--primary) 0%, var(--secondary) 100%);
  color: white;
  padding: 60px 20px;
  text-align: center;
  margin-bottom: 40px;
}

.hero .wrap {
  max-width: 1000px;
}

.hero h1 {
  font-size: clamp(2rem, 7vw, 3.5rem);
  margin: 0 0 12px 0;
  font-weight: 800;
  letter-spacing: -1px;
}

.hero > .wrap > p {
  font-size: clamp(1rem, 3vw, 1.3rem);
  margin: 0 0 40px 0;
  opacity: 0.95;
  font-weight: 500;
}

.hero-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(200px, 1fr));
  gap: 20px;
  margin-top: 40px;
}
.featured {
  padding: 36px 0;
  background: linear-gradient(180deg, rgba(255,255,255,0.02), transparent);
}
.featured .wrap {
  max-width: 1100px;
  margin: 0 auto;
  padding: 0 18px;
}
.featured h2 {
  font-size: 1.6rem;
  margin-bottom: 6px;
}
.featured .lead {
  color: var(--muted);
  margin-bottom: 18px;
}
.featured-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(220px, 1fr));
  gap: 14px;
}
.featured-card {
  display: block;
  background: var(--card-bg);
  padding: 14px;
  border-radius: 10px;
  box-shadow: 0 6px 18px rgba(8,13,26,0.06);
  text-decoration: none;
  color: inherit;
  transition: transform .28s var(--ease), box-shadow .28s var(--ease);
  overflow: hidden;
  will-change: transform;
  opacity: 0;
  transform: translateY(10px);
}
.featured-card:hover {
  transform: translateY(-6px);
  box-shadow: 0 12px 36px rgba(8,13,26,0.08);
}
.featured-card h3 { margin: 8px 0 6px; font-size: 1.05rem; }
.featured-card p { margin: 0; color: var(--muted); font-size: .92rem; }
.fc-icon { font-size: 1.3rem; width: 44px; height: 44px; display:inline-flex; align-items:center; justify-content:center; border-radius:8px; margin-right:8px; background: linear-gradient(135deg, var(--accent), rgba(0,0,0,0.03)); }

/* Animations */
@keyframes fadeUp {
  from { opacity: 0; transform: translateY(12px); }
  to { opacity: 1; transform: translateY(0); }
}
.animate-fade-up {
  animation: fadeUp .6s cubic-bezier(.2,.9,.2,1) both;
}

/* small hover pulse for interactive feel */
.card .card-cta, .featured-card:hover .fc-icon { transform-origin: center; }
.featured-card:hover .fc-icon { transform: scale(1.06); transition: transform .28s var(--ease); }

/* Buttons */
.btn { display: inline-block; padding: 10px 14px; border-radius: 8px; text-decoration: none; font-weight:600; }
.btn-primary { background: linear-gradient(90deg,var(--accent), #6c9cff); color: #fff; box-shadow: 0 8px 24px rgba(59,130,246,0.12); transition: transform .18s var(--ease), box-shadow .18s var(--ease); }
.btn-primary:hover { transform: translateY(-3px); box-shadow: 0 14px 40px rgba(59,130,246,0.12); }

/* Reveal helpers already present - ensure featured/reveal interplay */
.reveal.visible { opacity: 1; transform: none; }

.hero-card {
  display: block;
  text-decoration: none;
  color: inherit;
  background: rgba(255, 255, 255, 0.15);
  backdrop-filter: blur(10px);
  padding: 24px;
  border-radius: var(--radius-lg);
  border: 1px solid rgba(255, 255, 255, 0.2);
  transition: all 0.3s ease;
  cursor: pointer;
  animation: float 10s ease-in-out infinite alternate;
}

.hero-card:hover {
  background: rgba(255, 255, 255, 0.25);
  transform: translateY(-4px);
  border-color: rgba(255, 255, 255, 0.4);
}

.hero-card .icon {
  font-size: 2.5rem;
  display: block;
  margin-bottom: 12px;
}

.hero-card h3 {
  margin: 12px 0 8px 0;
  font-size: 1.2rem;
  font-weight: 700;
}

.hero-card p {
  margin: 0;
  font-size: 0.9rem;
  opacity: 0.9;
}

@keyframes float {
  0% { transform: translateY(0); }
  100% { transform: translateY(-6px); }
}

.featured {
  padding: 40px 20px 16px;
  background: linear-gradient(180deg, rgba(219, 234, 254, 0.45), rgba(255, 255, 255, 0));
}

.section-header h2 {
  margin: 4px 0 8px 0;
  font-size: clamp(1.8rem, 5vw, 2.2rem);
  font-weight: 800;
}

.eyebrow {
  display: inline-block;
  padding: 6px 12px;
  background: var(--primary-light);
  color: var(--primary-dark);
  border-radius: 999px;
  font-weight: 700;
  font-size: 0.85rem;
  letter-spacing: 0.4px;
  text-transform: uppercase;
}

.featured-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(220px, 1fr));
  gap: 16px;
  margin-top: 16px;
}

.featured-card {
  position: relative;
  background: var(--card);
  padding: 18px;
  border-radius: var(--radius-lg);
  box-shadow: var(--shadow-md);
  border: 1px solid var(--border);
  text-decoration: none;
  color: inherit;
  display: flex;
  flex-direction: column;
  gap: 6px;
  transition: transform 0.25s ease, box-shadow 0.25s ease, border-color 0.25s ease;
}

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

.featured-card h4 {
  margin: 0;
  font-size: 1.05rem;
  font-weight: 700;
}

.featured-card p {
  margin: 0;
  color: var(--text-muted);
  font-size: 0.95rem;
}

.featured-meta {
  display: flex;
  align-items: center;
  gap: 8px;
  color: var(--text-muted);
  font-size: 0.9rem;
  margin-top: 6px;
}

.content-header {
  margin-bottom: 32px;
}

.content-header h2 {
  margin: 0 0 12px 0;
  font-size: clamp(1.8rem, 5vw, 2.2rem);
  font-weight: 800;
  color: var(--text-primary);
}

.category-link {
  color: inherit;
  text-decoration: none;
}

.wrap {
  max-width: var(--max);
  margin: 0 auto;
  padding: 0 20px;
}

/* Header Styling */
.site-header {
  background: var(--card);
  border-bottom: 1px solid var(--border);
  box-shadow: var(--shadow-sm);
  position: sticky;
  top: 0;
  z-index: 100;
  backdrop-filter: blur(10px);
  background-color: rgba(255, 255, 255, 0.95);
}

.site-header .wrap {
  display: flex;
  gap: 16px;
  align-items: center;
  padding: 16px 20px;
}

.brand {
  font-weight: 800;
  background: linear-gradient(135deg, var(--primary) 0%, var(--secondary) 100%);
  -webkit-background-clip: text;
  -webkit-text-fill-color: transparent;
  background-clip: text;
  text-decoration: none;
  font-size: 1.5rem;
  letter-spacing: -0.5px;
  flex-shrink: 0;
}

.search {
  flex: 1;
  padding: 10px 14px;
  border-radius: 8px;
  border: 1px solid var(--border);
  background: var(--bg);
  color: var(--text-primary);
  font-size: 0.95rem;
  transition: all 0.3s ease;
}

.search:focus {
  outline: none;
  border-color: var(--primary);
  background: var(--card);
  box-shadow: 0 0 0 3px var(--primary-light);
}

.search::placeholder {
  color: var(--text-muted);
}

/* Main Grid Layout */
.main-grid {
  display: grid;
  grid-template-columns: 240px 1fr;
  gap: 32px;
  padding: 32px 20px;
  align-items: start;
}

/* Sidebar */
.sidebar {
  background: var(--card);
  padding: 20px;
  border-radius: var(--radius-lg);
  box-shadow: var(--shadow-md);
  height: fit-content;
  position: sticky;
  top: 80px;
}

.sidebar h3 {
  margin: 0 0 16px 0;
  font-size: 1.1rem;
  font-weight: 700;
  color: var(--text-primary);
  text-transform: uppercase;
  letter-spacing: 0.5px;
}

.sidebar ul {
  list-style: none;
  padding: 0;
  margin: 0;
}

.sidebar li {
  margin: 8px 0;
}

.sidebar a {
  display: block;
  padding: 10px 12px;
  color: var(--text-muted);
  text-decoration: none;
  border-radius: 8px;
  transition: all 0.3s ease;
  font-weight: 500;
  border-left: 3px solid transparent;
}

.sidebar a:hover {
  color: var(--primary);
  background: var(--primary-light);
  border-left-color: var(--primary);
  padding-left: 14px;
}

/* Cards Grid */
.cards-grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(260px, 1fr));
  gap: 20px;
}

.card {
  background: var(--card);
  padding: 20px;
  border-radius: var(--radius-lg);
  box-shadow: var(--shadow-md);
  border: 1px solid var(--border);
  transition: all 0.3s cubic-bezier(0.4, 0, 0.2, 1);
  cursor: pointer;
  display: flex;
  flex-direction: column;
  gap: 10px;
  text-decoration: none;
  color: inherit;
}

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

.card h4 {
  margin: 0;
  font-size: 1.1rem;
  font-weight: 700;
  color: var(--text-primary);
}

.card p {
  margin: 0;
  color: var(--text-muted);
  font-size: 0.95rem;
  line-height: 1.5;
}

.card::before {
  content: '';
  position: absolute;
  top: 0;
  left: 0;
  right: 0;
  height: 3px;
  background: linear-gradient(90deg, var(--primary), var(--secondary));
  border-radius: var(--radius-lg) var(--radius-lg) 0 0;
  opacity: 0;
  transition: opacity 0.3s ease;
}

.card:hover::before {
  opacity: 1;
}

.lead {
  color: var(--text-muted);
  font-size: 1rem;
  line-height: 1.6;
}

/* Footer */
.site-footer {
  margin-top: 48px;
  padding: 32px 20px;
  background: linear-gradient(135deg, var(--bg-dark) 0%, #0f172a 100%);
  border-top: 1px solid var(--border);
  color: #cbd5e1;
  text-align: center;
}

/* Calculator Page Styling */
article {
  display: flex;
  flex-direction: column;
  gap: 32px;
}

.calculator-hero {
  display: flex;
  flex-direction: column;
  gap: 16px;
  padding: 40px;
  background: linear-gradient(135deg, var(--primary) 0%, var(--secondary) 100%);
  border-radius: var(--radius-lg);
  color: white;
  box-shadow: var(--shadow-lg);
}

.calculator-hero h1 {
  margin: 0;
  font-size: clamp(1.8rem, 5vw, 2.5rem);
  font-weight: 800;
  letter-spacing: -0.5px;
}

.calculator-hero .lead {
  color: rgba(255, 255, 255, 0.9);
  font-size: 1.1rem;
  margin: 0;
}

/* Calculator Main Section */
.calculator-main {
  margin-top: 20px;
  background: var(--card);
  padding: 28px;
  border-radius: var(--radius-lg);
  box-shadow: var(--shadow-md);
  border: 1px solid var(--border);
}

.form-row {
  display: flex;
  gap: 12px;
  flex-wrap: wrap;
  align-items: flex-end;
}

.form-row input,
.form-row select {
  padding: 12px 14px;
  border-radius: 8px;
  border: 1px solid var(--border);
  background: var(--bg);
  color: var(--text-primary);
  font-size: 0.95rem;
  font-family: inherit;
  min-width: 140px;
  transition: all 0.3s ease;
}

.form-row input:focus,
.form-row select:focus {
  outline: none;
  border-color: var(--primary);
  background: var(--card);
  box-shadow: 0 0 0 3px var(--primary-light);
}

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

.btn {
  background: linear-gradient(135deg, var(--primary) 0%, var(--primary-dark) 100%);
  color: white;
  padding: 12px 24px;
  border-radius: 8px;
  border: none;
  cursor: pointer;
  font-weight: 600;
  font-size: 0.95rem;
  transition: all 0.3s ease;
  box-shadow: var(--shadow-md);
  letter-spacing: 0.3px;
}

.btn:hover {
  transform: translateY(-2px);
  box-shadow: var(--shadow-lg);
}

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

.result {
  margin-top: 16px;
  padding: 16px;
  background: linear-gradient(135deg, var(--primary-light) 0%, rgba(59, 130, 246, 0.05) 100%);
  border-left: 4px solid var(--primary);
  border-radius: 8px;
  font-weight: 500;
  color: var(--text-primary);
}

/* Explanation, Formula, FAQs Sections */
.explanation,
.formula,
.faqs {
  background: var(--card);
  padding: 24px;
  border-radius: var(--radius-lg);
  box-shadow: var(--shadow-md);
  border: 1px solid var(--border);
}

.explanation h2,
.formula h3,
.faqs h3 {
  margin-top: 0;
  color: var(--text-primary);
  font-size: clamp(1.3rem, 3vw, 1.5rem);
  font-weight: 700;
}

.explanation p {
  color: var(--text-muted);
  line-height: 1.8;
  margin: 0;
}

.formula pre {
  background: var(--bg);
  padding: 16px;
  border-radius: 8px;
  overflow-x: auto;
  border: 1px solid var(--border);
  color: var(--primary);
  font-size: 0.95rem;
  line-height: 1.6;
}

/* FAQ Details */
.faqs details {
  margin: 12px 0;
  border: 1px solid var(--border);
  border-radius: 8px;
  padding: 0;
  transition: all 0.3s ease;
}

.faqs details:hover {
  border-color: var(--primary);
  box-shadow: var(--shadow-sm);
}

.faqs summary {
  padding: 14px 16px;
  cursor: pointer;
  font-weight: 600;
  color: var(--text-primary);
  user-select: none;
  display: flex;
  justify-content: space-between;
  align-items: center;
}

.faqs summary:hover {
  background: var(--bg);
  color: var(--primary);
}

.faqs details[open] summary {
  background: var(--primary-light);
  color: var(--primary);
  border-bottom: 1px solid var(--border);
}

.faqs details p {
  margin: 0;
  padding: 12px 16px;
  color: var(--text-muted);
  line-height: 1.6;
}

/* Responsive Design */
@media (max-width: 1024px) {
  .main-grid {
    grid-template-columns: 200px 1fr;
    gap: 24px;
    padding: 24px 16px;
  }

  .cards-grid {
    grid-template-columns: repeat(auto-fill, minmax(220px, 1fr));
  }
}

@media (max-width: 768px) {
  .main-grid {
    grid-template-columns: 1fr;
    gap: 24px;
    padding: 16px;
  }

  .sidebar {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(140px, 1fr));
    gap: 12px;
    height: auto;
    position: static;
    top: auto;
    padding: 16px;
  }

  .sidebar h3 {
    grid-column: 1 / -1;
  }

  .sidebar a {
    text-align: center;
    padding: 8px 10px;
  }

  .cards-grid {
    grid-template-columns: repeat(auto-fill, minmax(180px, 1fr));
    gap: 16px;
  }

  .site-header .wrap {
    gap: 12px;
    padding: 12px 16px;
  }

  .brand {
    font-size: 1.25rem;
  }

  .search {
    font-size: 0.9rem;
    padding: 8px 12px;
  }

  .calculator-hero {
    padding: 24px;
  }

  .calculator-hero h1 {
    font-size: 1.8rem;
  }

  .calculator-main {
    padding: 20px;
  }

  .form-row {
    flex-direction: column;
  }

  .form-row input,
  .form-row select,
  .btn {
    width: 100%;
    min-width: unset;
  }
}

@media (max-width: 640px) {
  .main-grid {
    padding: 12px;
  }

  .sidebar {
    grid-template-columns: repeat(2, 1fr);
  }

  .cards-grid {
    grid-template-columns: 1fr;
    gap: 12px;
  }

  .site-header {
    position: relative;
  }

  .site-header .wrap {
    flex-direction: column;
    gap: 10px;
  }

  .search {
    width: 100%;
  }

  .brand {
    font-size: 1.15rem;
  }

  .calculator-hero {
    padding: 16px;
    gap: 12px;
  }

  .calculator-hero h1 {
    font-size: 1.5rem;
  }

  .calculator-hero .lead {
    font-size: 0.95rem;
  }

  .calculator-main {
    padding: 16px;
  }

  .explanation,
  .formula,
  .faqs {
    padding: 16px;
  }

  .explanation h2,
  .formula h3,
  .faqs h3 {
    font-size: 1.2rem;
  }

  .formula pre {
    font-size: 0.85rem;
    padding: 12px;
  }

  .faqs summary {
    padding: 12px 14px;
    font-size: 0.95rem;
  }

  .faqs details p {
    padding: 10px 14px;
    font-size: 0.9rem;
  }

  article {
    gap: 20px;
  }
}

@media (max-width: 480px) {
  :root {
    font-size: 14px;
  }

  .site-header .wrap {
    padding: 10px 12px;
  }

  .brand {
    font-size: 1rem;
  }

  .search {
    display: none;
  }

  .cards-grid {
    gap: 10px;
  }

  .card {
    padding: 16px;
  }

  .calculator-hero {
    padding: 12px;
  }

  .calculator-hero h1 {
    font-size: 1.3rem;
  }

  .calculator-main {
    padding: 12px;
  }

  .form-row {
    gap: 8px;
  }

  .form-row input,
  .form-row select,
  .btn {
    padding: 10px 12px;
    font-size: 0.9rem;
  }
}

/* Final mobile tuning for hero, cards and sidebar */
@media (max-width: 640px) {
  .hero { padding: 28px 12px; }
  .hero h1 { font-size: 1.6rem; }
  .hero > .wrap > p { font-size: 1rem; }
  .hero-grid { gap: 12px; }
  .featured { padding: 20px 0 8px; }
  .featured .wrap { padding: 0 12px; }
  .cards-grid { gap: 12px; }
  .sidebar { padding: 10px; }
}

/* Brand logo and header alignment */
.brand {
  display: inline-flex;
  align-items: center;
  gap: 10px;
  text-decoration: none;
  color: var(--primary);
  font-weight: 700;
}

.brand-logo {
  width: 36px;
  height: 36px;
  object-fit: contain;
  display: inline-block;
}

.brand-text { font-weight:700; color:inherit; }


/* Sidebar polish overrides - final touch */
.sidebar {
  background: var(--card);
  padding: 18px;
  border-radius: var(--radius-lg);
  box-shadow: var(--shadow-md);
  align-self: start;
  position: sticky;
  top: 96px;
  display: block;
}

.sidebar h3 {
  margin: 0 0 12px 0;
  font-size: 0.95rem;
  letter-spacing: 0.6px;
  color: var(--text-primary);
  text-transform: uppercase;
}

.sidebar nav ul {
  list-style: none;
  margin: 0;
  padding: 0;
  display: flex;
  flex-direction: column;
  gap: 10px;
}

.sidebar nav a {
  display: inline-flex;
  align-items: center;
  gap: 10px;
  padding: 8px 10px;
  border-radius: 8px;
  text-decoration: none;
  color: var(--text-primary);
  transition: background .18s ease, transform .12s ease, color .18s ease;
  font-weight: 500;
}

.sidebar nav a .icon {
  font-size: 1.15rem;
  line-height: 1;
}

.sidebar nav a:hover,
.sidebar nav a:focus {
  background: var(--primary-light);
  color: var(--primary);
  transform: translateY(-2px);
  outline: none;
}

.sidebar nav a.active,
.sidebar nav a[aria-current="true"] {
  font-weight: 700;
  color: var(--primary);
  background: linear-gradient(90deg, rgba(59,130,246,0.06), rgba(139,92,246,0.03));
}

/* On small screens, keep sidebar compact and remove sticky */
@media (max-width: 768px) {
  .sidebar {
    position: static;
    top: auto;
    padding: 12px;
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(120px, 1fr));
    gap: 10px;
  }

  .sidebar h3 { grid-column: 1 / -1; }

  .sidebar nav a { justify-content: center; padding: 8px; }
}