:root {
  --primary: #2563eb;
  --primary-dark: #1d4ed8;
  --primary-light: #eff6ff;
  --secondary: #0f172a;
  --text-main: #1e293b;
  --text-muted: #64748b;
  --bg-light: #f8fafc;
  --card-bg: #ffffff;
  --border: #e2e8f0;
  --border-focus: #3b82f6;
  --success: #16a34a;
  --success-bg: #f0fdf4;
  --warning: #f59e0b;
  --warning-bg: #fffbeb;
  --radius: 12px;
  --radius-lg: 18px;
  --shadow-sm: 0 1px 2px 0 rgba(0, 0, 0, 0.05);
  --shadow: 0 4px 6px -1px rgba(0, 0, 0, 0.07), 0 2px 4px -2px rgba(0, 0, 0, 0.05);
  --shadow-lg: 0 10px 25px -5px rgba(15, 23, 42, 0.08), 0 8px 10px -6px rgba(15, 23, 42, 0.04);
}

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

body {
  font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, "Helvetica Neue", Arial, sans-serif;
  color: var(--text-main);
  background-color: #ffffff;
  line-height: 1.65;
  -webkit-font-smoothing: antialiased;
}

a {
  color: var(--primary);
  text-decoration: none;
  transition: color 0.15s ease;
}

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

.container {
  max-width: 1140px;
  margin: 0 auto;
  padding: 0 20px;
}

/* Topbar */
.topbar {
  background: var(--secondary);
  color: #94a3b8;
  padding: 8px 0;
  font-size: 13px;
  border-bottom: 1px solid #1e293b;
}

.topbar .container {
  display: flex;
  justify-content: space-between;
  align-items: center;
  flex-wrap: wrap;
  gap: 10px;
}

.topbar a {
  color: #cbd5e1;
}

/* Navbar */
.navbar {
  position: sticky;
  top: 0;
  z-index: 100;
  background: rgba(255, 255, 255, 0.98);
  backdrop-filter: blur(8px);
  border-bottom: 1px solid var(--border);
}

.navwrap {
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: 16px 20px;
}

.logo {
  font-size: 24px;
  font-weight: 800;
  color: var(--secondary);
  display: flex;
  align-items: center;
  gap: 6px;
  text-decoration: none !important;
}

.logo span {
  color: var(--primary);
}

.navlinks {
  display: flex;
  align-items: center;
  gap: 22px;
}

.navlinks a {
  color: #334155;
  font-weight: 600;
  font-size: 15px;
  padding: 6px 4px;
  position: relative;
  text-decoration: none;
}

.navlinks a:hover,
.navlinks a.active {
  color: var(--primary);
}

.navlinks a.active::after {
  content: "";
  position: absolute;
  bottom: -4px;
  left: 0;
  right: 0;
  height: 2px;
  background: var(--primary);
  border-radius: 2px;
}

.nav-cta {
  background: var(--primary);
  color: #ffffff !important;
  padding: 8px 16px !important;
  border-radius: 8px;
  font-weight: 600;
}

.nav-cta:hover {
  background: var(--primary-dark);
  text-decoration: none !important;
}

.mobile-toggle {
  display: none;
  background: none;
  border: 1px solid var(--border);
  border-radius: 8px;
  padding: 8px 12px;
  cursor: pointer;
  font-size: 18px;
  color: var(--secondary);
}

/* Hero */
.hero {
  background: linear-gradient(135deg, #f0f7ff 0%, #ffffff 50%, #f4f8ff 100%);
  padding: 60px 0 50px;
  border-bottom: 1px solid var(--border);
}

.hero-grid {
  display: grid;
  grid-template-columns: 1.15fr 0.85fr;
  gap: 40px;
  align-items: center;
}

.badge {
  display: inline-flex;
  align-items: center;
  gap: 6px;
  background: var(--primary-light);
  color: var(--primary);
  border: 1px solid #bfdbfe;
  border-radius: 9999px;
  padding: 5px 14px;
  font-size: 13px;
  font-weight: 700;
  margin-bottom: 16px;
}

.hero h1 {
  font-size: 42px;
  line-height: 1.15;
  font-weight: 800;
  color: var(--secondary);
  margin-bottom: 18px;
  letter-spacing: -0.02em;
}

.hero p {
  font-size: 17px;
  color: var(--text-muted);
  margin-bottom: 24px;
  line-height: 1.6;
}

.btns {
  display: flex;
  gap: 12px;
  flex-wrap: wrap;
}

.btn {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  gap: 8px;
  padding: 12px 22px;
  border-radius: 10px;
  font-size: 15px;
  font-weight: 700;
  cursor: pointer;
  border: none;
  transition: all 0.15s ease;
  text-decoration: none !important;
}

.btn-primary {
  background: var(--primary);
  color: #ffffff;
  box-shadow: 0 4px 10px rgba(37, 99, 235, 0.25);
}

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

.btn-outline {
  background: #ffffff;
  color: var(--secondary);
  border: 1px solid var(--border);
}

.btn-outline:hover {
  background: var(--bg-light);
  border-color: #cbd5e1;
}

.btn-sm {
  padding: 8px 14px;
  font-size: 13px;
  border-radius: 8px;
}

.hero-card {
  background: #ffffff;
  border: 1px solid var(--border);
  border-radius: var(--radius-lg);
  padding: 24px;
  box-shadow: var(--shadow-lg);
}

.hero-features {
  display: flex;
  flex-direction: column;
  gap: 14px;
}

.feature-item {
  display: flex;
  align-items: flex-start;
  gap: 14px;
  padding: 10px;
  border-radius: var(--radius);
  transition: background 0.15s ease;
}

.feature-item:hover {
  background: var(--bg-light);
}

.feature-icon {
  width: 40px;
  height: 40px;
  border-radius: 10px;
  background: var(--primary-light);
  color: var(--primary);
  display: flex;
  align-items: center;
  justify-content: center;
  font-weight: 800;
  font-size: 18px;
  flex-shrink: 0;
}

.feature-text h4 {
  font-size: 16px;
  font-weight: 700;
  color: var(--secondary);
  margin-bottom: 2px;
}

.feature-text p {
  font-size: 13px;
  color: var(--text-muted);
  line-height: 1.4;
  margin: 0;
}

/* Sections */
.section {
  padding: 60px 0;
}

.section-alt {
  background: var(--bg-light);
}

.section-header {
  text-align: center;
  max-width: 760px;
  margin: 0 auto 40px;
}

.section-header h2 {
  font-size: 32px;
  font-weight: 800;
  color: var(--secondary);
  margin-bottom: 12px;
  letter-spacing: -0.01em;
}

.section-header p {
  font-size: 17px;
  color: var(--text-muted);
}

.section-header .tag {
  display: inline-block;
  background: #e0e7ff;
  color: #3730a3;
  padding: 4px 12px;
  border-radius: 9999px;
  font-size: 12px;
  font-weight: 700;
  margin-bottom: 10px;
  text-transform: uppercase;
  letter-spacing: 0.05em;
}

/* Cards & Grid */
.grid-3 {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  gap: 24px;
}

.grid-2 {
  display: grid;
  grid-template-columns: repeat(2, 1fr);
  gap: 28px;
}

.grid-4 {
  display: grid;
  grid-template-columns: repeat(4, 1fr);
  gap: 20px;
}

.card {
  background: var(--card-bg);
  border: 1px solid var(--border);
  border-radius: var(--radius-lg);
  padding: 26px;
  box-shadow: var(--shadow-sm);
  transition: transform 0.2s ease, box-shadow 0.2s ease, border-color 0.2s ease;
  display: flex;
  flex-direction: column;
}

.card:hover {
  transform: translateY(-3px);
  box-shadow: var(--shadow);
  border-color: #cbd5e1;
}

.card-icon {
  width: 48px;
  height: 48px;
  border-radius: 12px;
  background: var(--primary-light);
  color: var(--primary);
  display: flex;
  align-items: center;
  justify-content: center;
  font-size: 22px;
  margin-bottom: 16px;
}

.card h3 {
  font-size: 20px;
  font-weight: 700;
  color: var(--secondary);
  margin-bottom: 10px;
}

.card p {
  font-size: 15px;
  color: var(--text-muted);
  line-height: 1.6;
  margin-bottom: 16px;
  flex-grow: 1;
}

.card-footer {
  margin-top: auto;
  padding-top: 14px;
  border-top: 1px solid #f1f5f9;
  display: flex;
  align-items: center;
  justify-content: space-between;
}

/* Calculator Component */
.calc-widget {
  background: #ffffff;
  border: 1px solid var(--border);
  border-radius: var(--radius-lg);
  box-shadow: var(--shadow-lg);
  overflow: hidden;
  margin: 30px 0;
}

.calc-tabs {
  display: flex;
  background: #f1f5f9;
  border-bottom: 1px solid var(--border);
  overflow-x: auto;
}

.calc-tab {
  padding: 14px 22px;
  background: none;
  border: none;
  font-size: 15px;
  font-weight: 700;
  color: #475569;
  cursor: pointer;
  white-space: nowrap;
  transition: all 0.15s ease;
  border-bottom: 3px solid transparent;
}

.calc-tab:hover {
  color: var(--primary);
  background: #e2e8f0;
}

.calc-tab.active {
  color: var(--primary);
  background: #ffffff;
  border-bottom-color: var(--primary);
}

.calc-body {
  padding: 30px;
}

.calc-pane {
  display: none;
}

.calc-pane.active {
  display: block;
}

.calc-grid {
  display: grid;
  grid-template-columns: 1.1fr 0.9fr;
  gap: 30px;
  align-items: start;
}

.form-group {
  margin-bottom: 20px;
}

.form-label {
  display: block;
  font-size: 14px;
  font-weight: 700;
  color: var(--secondary);
  margin-bottom: 8px;
}

.input-with-affix {
  display: flex;
  align-items: center;
  border: 1px solid var(--border);
  border-radius: 8px;
  background: #ffffff;
  overflow: hidden;
  transition: border-color 0.15s ease;
}

.input-with-affix:focus-within {
  border-color: var(--border-focus);
  box-shadow: 0 0 0 3px rgba(37, 99, 235, 0.15);
}

.input-affix {
  padding: 10px 14px;
  background: #f8fafc;
  color: #64748b;
  font-weight: 600;
  font-size: 14px;
  border-right: 1px solid var(--border);
}

.input-affix.suffix {
  border-right: none;
  border-left: 1px solid var(--border);
}

.form-control {
  width: 100%;
  padding: 11px 14px;
  font-size: 15px;
  border: none;
  outline: none;
  color: var(--secondary);
  font-family: inherit;
}

.radio-group {
  display: flex;
  gap: 12px;
  margin-top: 6px;
}

.radio-label {
  display: flex;
  align-items: center;
  gap: 8px;
  padding: 8px 14px;
  border: 1px solid var(--border);
  border-radius: 8px;
  cursor: pointer;
  font-size: 14px;
  font-weight: 600;
  background: #ffffff;
  transition: all 0.15s ease;
}

.radio-label:hover {
  background: var(--bg-light);
}

.radio-label input[type="radio"] {
  accent-color: var(--primary);
}

.pill-group {
  display: flex;
  gap: 8px;
  flex-wrap: wrap;
  margin-top: 8px;
}

.pill-btn {
  padding: 6px 14px;
  border: 1px solid var(--border);
  border-radius: 6px;
  background: #ffffff;
  font-size: 13px;
  font-weight: 600;
  color: #334155;
  cursor: pointer;
  transition: all 0.15s ease;
}

.pill-btn:hover,
.pill-btn.active {
  background: var(--primary-light);
  border-color: #93c5fd;
  color: var(--primary-dark);
}

.result-card {
  background: linear-gradient(135deg, #0f172a 0%, #1e293b 100%);
  color: #ffffff;
  border-radius: var(--radius);
  padding: 24px;
  box-shadow: var(--shadow);
}

.result-card h4 {
  font-size: 14px;
  text-transform: uppercase;
  letter-spacing: 0.08em;
  color: #94a3b8;
  margin-bottom: 14px;
}

.result-main {
  margin-bottom: 20px;
  padding-bottom: 16px;
  border-bottom: 1px solid #334155;
}

.result-main .label {
  font-size: 14px;
  color: #cbd5e1;
}

.result-main .val {
  font-size: 36px;
  font-weight: 800;
  color: #60a5fa;
  line-height: 1.2;
}

.result-breakdown {
  display: flex;
  flex-direction: column;
  gap: 10px;
  font-size: 14px;
}

.breakdown-row {
  display: flex;
  justify-content: space-between;
  align-items: center;
  color: #cbd5e1;
}

.breakdown-row strong {
  color: #ffffff;
}

.copy-btn {
  margin-top: 18px;
  width: 100%;
  background: #334155;
  color: #ffffff;
  border: none;
  padding: 10px;
  border-radius: 8px;
  font-size: 14px;
  font-weight: 600;
  cursor: pointer;
  display: flex;
  align-items: center;
  justify-content: center;
  gap: 6px;
  transition: background 0.15s ease;
}

.copy-btn:hover {
  background: #475569;
}

/* Articles and Content */
.article {
  max-width: 860px;
  margin: 0 auto;
}

.breadcrumb {
  font-size: 14px;
  color: var(--text-muted);
  margin-bottom: 20px;
}

.article-header {
  margin-bottom: 30px;
  padding-bottom: 20px;
  border-bottom: 1px solid var(--border);
}

.article-header h1 {
  font-size: 36px;
  line-height: 1.2;
  font-weight: 800;
  color: var(--secondary);
  margin-bottom: 14px;
}

.article-meta {
  display: flex;
  align-items: center;
  gap: 16px;
  font-size: 14px;
  color: var(--text-muted);
  flex-wrap: wrap;
}

.article-content {
  font-size: 17px;
  line-height: 1.8;
  color: #334155;
}

.article-content h2 {
  font-size: 26px;
  font-weight: 800;
  color: var(--secondary);
  margin: 36px 0 16px;
  line-height: 1.3;
}

.article-content h3 {
  font-size: 20px;
  font-weight: 700;
  color: var(--secondary);
  margin: 26px 0 12px;
}

.article-content p {
  margin-bottom: 20px;
}

.article-content ul,
.article-content ol {
  margin-bottom: 24px;
  padding-left: 24px;
}

.article-content li {
  margin-bottom: 10px;
}

.formula-box {
  background: #f8fafc;
  border-left: 4px solid var(--primary);
  padding: 18px 22px;
  border-radius: 0 10px 10px 0;
  margin: 24px 0;
  font-family: monospace;
  font-size: 15px;
  color: #1e293b;
}

.content-table {
  width: 100%;
  border-collapse: collapse;
  margin: 28px 0;
  font-size: 15px;
  border-radius: 10px;
  overflow: hidden;
  border: 1px solid var(--border);
}

.content-table th,
.content-table td {
  padding: 14px 16px;
  text-align: left;
  border-bottom: 1px solid var(--border);
}

.content-table th {
  background: #f1f5f9;
  font-weight: 700;
  color: var(--secondary);
}

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

.content-table tr:hover {
  background: #f8fafc;
}

.author-box {
  background: var(--bg-light);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 24px;
  margin: 40px 0 20px;
  display: flex;
  align-items: center;
  gap: 20px;
}

.author-avatar {
  width: 60px;
  height: 60px;
  border-radius: 50%;
  background: var(--primary);
  color: #ffffff;
  display: flex;
  align-items: center;
  justify-content: center;
  font-weight: 800;
  font-size: 22px;
  flex-shrink: 0;
}

.author-info h4 {
  font-size: 17px;
  font-weight: 700;
  color: var(--secondary);
  margin-bottom: 4px;
}

.author-info p {
  font-size: 14px;
  color: var(--text-muted);
  line-height: 1.5;
  margin: 0;
}

/* FAQ Details */
.faq-list {
  display: flex;
  flex-direction: column;
  gap: 12px;
  max-width: 860px;
  margin: 0 auto;
}

.faq-item {
  border: 1px solid var(--border);
  border-radius: var(--radius);
  background: #ffffff;
  overflow: hidden;
  transition: border-color 0.15s ease;
}

.faq-item summary {
  padding: 18px 22px;
  font-weight: 700;
  font-size: 17px;
  cursor: pointer;
  color: var(--secondary);
  list-style: none;
  display: flex;
  justify-content: space-between;
  align-items: center;
}

.faq-item summary::-webkit-details-marker {
  display: none;
}

.faq-item summary::after {
  content: "+";
  font-size: 20px;
  font-weight: 600;
  color: var(--primary);
}

.faq-item[open] summary::after {
  content: "−";
}

.faq-item[open] summary {
  border-bottom: 1px solid #f1f5f9;
}

.faq-content {
  padding: 18px 22px;
  color: #475569;
  font-size: 15px;
  line-height: 1.7;
}

/* Footer */
.footer {
  background: var(--secondary);
  color: #94a3b8;
  padding: 50px 0 25px;
  border-top: 1px solid #1e293b;
}

.footer-grid {
  display: grid;
  grid-template-columns: 2fr 1fr 1fr 1.2fr;
  gap: 36px;
  margin-bottom: 40px;
}

.footer-col h4 {
  color: #ffffff;
  font-size: 16px;
  font-weight: 700;
  margin-bottom: 18px;
}

.footer-links {
  list-style: none;
  display: flex;
  flex-direction: column;
  gap: 10px;
}

.footer-links a {
  color: #cbd5e1;
  font-size: 14px;
  text-decoration: none;
}

.footer-links a:hover {
  color: #ffffff;
  text-decoration: underline;
}

.footer-bottom {
  padding-top: 24px;
  border-top: 1px solid #1e293b;
  display: flex;
  justify-content: space-between;
  align-items: center;
  flex-wrap: wrap;
  gap: 14px;
  font-size: 13px;
}

/* Mobile & Responsive */
@media (max-width: 960px) {
  .hero-grid,
  .calc-grid,
  .grid-2 {
    grid-template-columns: 1fr;
  }
  
  .grid-3 {
    grid-template-columns: repeat(2, 1fr);
  }
  
  .grid-4 {
    grid-template-columns: repeat(2, 1fr);
  }

  .footer-grid {
    grid-template-columns: 1fr 1fr;
  }

  .hero h1 {
    font-size: 32px;
  }
}

@media (max-width: 768px) {
  .topbar {
    display: none;
  }

  .navlinks {
    display: none;
    position: absolute;
    top: 100%;
    left: 0;
    right: 0;
    background: #ffffff;
    flex-direction: column;
    padding: 18px 24px;
    border-bottom: 1px solid var(--border);
    box-shadow: var(--shadow-lg);
    gap: 14px;
    align-items: flex-start;
  }

  .navlinks.show {
    display: flex;
  }

  .mobile-toggle {
    display: block;
  }

  .grid-3,
  .grid-4,
  .footer-grid {
    grid-template-columns: 1fr;
  }

  .hero {
    padding: 36px 0;
  }

  .hero h1 {
    font-size: 28px;
  }

  .section {
    padding: 40px 0;
  }

  .calc-body {
    padding: 20px 16px;
  }

  .result-main .val {
    font-size: 28px;
  }
}