:root {
  --primary: #2563eb;
  --primary-dark: #1d4ed8;
  --primary-light: #eff6ff;
  --accent: #f97316;
  --accent-hover: #ea580c;
  --slate-900: #0f172a;
  --slate-800: #1e293b;
  --slate-700: #334155;
  --slate-600: #475569;
  --slate-500: #64748b;
  --slate-200: #e2e8f0;
  --slate-100: #f1f5f9;
  --slate-50: #f8fafc;
  --success: #16a34a;
  --surface: #ffffff;
  --radius-sm: 6px;
  --radius-md: 10px;
  --radius-lg: 16px;
  --shadow-sm: 0 1px 2px 0 rgb(0 0 0 / 0.05);
  --shadow-md: 0 4px 6px -1px rgb(0 0 0 / 0.1), 0 2px 4px -2px rgb(0 0 0 / 0.1);
  --shadow-lg: 0 10px 15px -3px rgb(0 0 0 / 0.1), 0 4px 6px -4px rgb(0 0 0 / 0.1);
  --max-w: 1120px;
}

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

body {
  font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Helvetica, Arial, sans-serif;
  color: var(--slate-800);
  background-color: var(--slate-50);
  line-height: 1.6;
  -webkit-font-smoothing: antialiased;
}

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

a:hover {
  text-decoration: underline;
}

/* Header & Nav */
header {
  background-color: var(--slate-900);
  color: #ffffff;
  position: sticky;
  top: 0;
  z-index: 50;
  box-shadow: var(--shadow-md);
}

.nav-container {
  max-width: var(--max-w);
  margin: 0 auto;
  padding: 0.875rem 1.25rem;
  display: flex;
  align-items: center;
  justify-content: space-between;
}

.brand {
  display: flex;
  align-items: center;
  gap: 0.75rem;
  color: #ffffff;
  text-decoration: none;
  font-weight: 700;
  font-size: 1.125rem;
}

.brand:hover {
  text-decoration: none;
}

.brand-icon {
  background: linear-gradient(135deg, var(--primary), var(--accent));
  width: 34px;
  height: 34px;
  border-radius: var(--radius-sm);
  display: flex;
  align-items: center;
  justify-content: center;
  font-weight: 900;
  font-size: 1rem;
  color: #ffffff;
}

.nav-links {
  display: flex;
  align-items: center;
  gap: 1.25rem;
}

.nav-link {
  color: var(--slate-200);
  font-size: 0.9375rem;
  font-weight: 500;
  transition: color 0.15s;
}

.nav-link:hover {
  color: #ffffff;
  text-decoration: none;
}

.btn {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  gap: 0.5rem;
  font-weight: 600;
  padding: 0.625rem 1.25rem;
  border-radius: var(--radius-md);
  cursor: pointer;
  transition: all 0.15s ease-in-out;
  border: none;
  text-decoration: none;
  font-size: 0.9375rem;
}

.btn:hover {
  text-decoration: none;
}

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

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

.btn-accent {
  background-color: var(--accent);
  color: #ffffff;
  box-shadow: 0 2px 4px rgba(249, 115, 22, 0.3);
}

.btn-accent:hover {
  background-color: var(--accent-hover);
}

.btn-outline {
  border: 1px solid var(--slate-200);
  background-color: var(--surface);
  color: var(--slate-700);
}

.btn-outline:hover {
  background-color: var(--slate-100);
  border-color: var(--slate-600);
}

.btn-lg {
  padding: 0.875rem 1.75rem;
  font-size: 1.0625rem;
  border-radius: var(--radius-md);
}

/* Hero Section */
.hero {
  background: linear-gradient(180deg, var(--slate-900) 0%, var(--slate-800) 100%);
  color: #ffffff;
  padding: 3.5rem 1.25rem;
  text-align: center;
}

.hero-inner {
  max-width: 800px;
  margin: 0 auto;
}

.hero-tagline {
  display: inline-block;
  background-color: rgba(249, 115, 22, 0.2);
  color: #fb923c;
  border: 1px solid rgba(249, 115, 22, 0.4);
  padding: 0.25rem 0.875rem;
  border-radius: 9999px;
  font-size: 0.8125rem;
  font-weight: 700;
  text-transform: uppercase;
  letter-spacing: 0.05em;
  margin-bottom: 1.25rem;
}

.hero h1 {
  font-size: 2.5rem;
  font-weight: 800;
  line-height: 1.2;
  margin-bottom: 1rem;
}

.hero p {
  font-size: 1.1875rem;
  color: var(--slate-200);
  margin-bottom: 2rem;
  max-width: 650px;
  margin-left: auto;
  margin-right: auto;
}

.hero-actions {
  display: flex;
  gap: 1rem;
  justify-content: center;
  flex-wrap: wrap;
}

.badge-row {
  display: flex;
  justify-content: center;
  align-items: center;
  gap: 1.5rem;
  margin-top: 2rem;
  font-size: 0.875rem;
  color: var(--slate-200);
}

.badge-item {
  display: flex;
  align-items: center;
  gap: 0.375rem;
}

/* Page Layout */
.main-container {
  max-width: var(--max-w);
  margin: 2rem auto;
  padding: 0 1.25rem;
}

/* Breadcrumbs */
.breadcrumbs {
  font-size: 0.875rem;
  color: var(--slate-500);
  margin-bottom: 1.5rem;
}

.breadcrumbs a {
  color: var(--slate-600);
}

.breadcrumbs span {
  margin: 0 0.375rem;
}

/* Calculator Grid */
.calc-layout {
  display: grid;
  grid-template-columns: 1fr;
  gap: 2rem;
  margin-bottom: 3rem;
}

@media (min-width: 840px) {
  .calc-layout {
    grid-template-columns: 1fr 1fr;
  }
}

.calc-card {
  background-color: var(--surface);
  border-radius: var(--radius-lg);
  border: 1px solid var(--slate-200);
  padding: 1.75rem;
  box-shadow: var(--shadow-sm);
}

.calc-header {
  margin-bottom: 1.5rem;
}

.calc-header h2 {
  font-size: 1.375rem;
  font-weight: 700;
  color: var(--slate-900);
  margin-bottom: 0.375rem;
}

.calc-header p {
  font-size: 0.875rem;
  color: var(--slate-500);
}

.form-group {
  margin-bottom: 1.25rem;
}

.form-group label {
  display: block;
  font-size: 0.875rem;
  font-weight: 600;
  color: var(--slate-700);
  margin-bottom: 0.375rem;
}

.form-row {
  display: flex;
  gap: 0.75rem;
}

.form-row .form-group {
  flex: 1;
}

.input-with-unit {
  position: relative;
  display: flex;
  align-items: center;
}

.input-control {
  width: 100%;
  padding: 0.625rem 0.875rem;
  font-size: 1rem;
  border: 1.5px solid var(--slate-200);
  border-radius: var(--radius-md);
  background-color: #ffffff;
  color: var(--slate-900);
  transition: border-color 0.15s, box-shadow 0.15s;
}

.input-control:focus {
  outline: none;
  border-color: var(--primary);
  box-shadow: 0 0 0 3px rgba(37, 99, 235, 0.15);
}

.input-unit {
  position: absolute;
  right: 0.875rem;
  color: var(--slate-500);
  font-size: 0.875rem;
  font-weight: 500;
  pointer-events: none;
}

.input-with-unit .input-control {
  padding-right: 2.5rem;
}

select.input-control {
  cursor: pointer;
  background-image: url("data:image/svg+xml,%3Csvg xmlns='http://www.w3.org/2000/svg' fill='none' viewBox='0 0 24 24' stroke='%2364748b'%3E%3Cpath stroke-linecap='round' stroke-linejoin='round' stroke-width='2' d='M19 9l-7 7-7-7'%3E%3C/path%3E%3C/svg%3E");
  background-repeat: no-repeat;
  background-position: right 0.75rem center;
  background-size: 1.25rem;
  appearance: none;
}

/* Results Panel */
.results-card {
  background-color: var(--surface);
  border: 2px solid var(--slate-900);
  border-radius: var(--radius-lg);
  padding: 1.75rem;
  box-shadow: var(--shadow-md);
  display: flex;
  flex-direction: column;
  justify-content: space-between;
}

.results-header {
  border-bottom: 1px solid var(--slate-200);
  padding-bottom: 1rem;
  margin-bottom: 1.25rem;
}

.results-title {
  font-size: 1.125rem;
  font-weight: 700;
  color: var(--slate-900);
  text-transform: uppercase;
  letter-spacing: 0.05em;
}

.result-hero {
  background-color: var(--slate-50);
  border-radius: var(--radius-md);
  padding: 1.25rem;
  text-align: center;
  margin-bottom: 1.25rem;
  border: 1px solid var(--slate-200);
}

.result-hero-label {
  font-size: 0.8125rem;
  font-weight: 600;
  color: var(--slate-500);
  text-transform: uppercase;
}

.result-hero-value {
  font-size: 2.25rem;
  font-weight: 800;
  color: var(--primary);
  line-height: 1.2;
  margin: 0.25rem 0;
}

.result-hero-sub {
  font-size: 0.875rem;
  color: var(--slate-600);
}

.result-metrics {
  display: flex;
  flex-direction: column;
  gap: 0.75rem;
  margin-bottom: 1.5rem;
}

.result-row {
  display: flex;
  justify-content: space-between;
  align-items: center;
  padding: 0.5rem 0;
  border-bottom: 1px dashed var(--slate-200);
  font-size: 0.9375rem;
}

.result-row:last-child {
  border-bottom: none;
}

.result-label {
  color: var(--slate-600);
}

.result-val {
  font-weight: 700;
  color: var(--slate-900);
}

.app-promo-box {
  background: linear-gradient(135deg, #f0fdf4 0%, #dcfce7 100%);
  border: 1.5px solid #86efac;
  border-radius: var(--radius-md);
  padding: 1.25rem;
  margin-top: 1.25rem;
  text-align: center;
}

.app-promo-box h4 {
  color: #166534;
  font-size: 1rem;
  font-weight: 700;
  margin-bottom: 0.375rem;
}

.app-promo-box p {
  color: #15803d;
  font-size: 0.8125rem;
  margin-bottom: 0.875rem;
}

/* Content Sections */
.article-section {
  background-color: var(--surface);
  border-radius: var(--radius-lg);
  border: 1px solid var(--slate-200);
  padding: 2.25rem;
  margin-bottom: 2.5rem;
  box-shadow: var(--shadow-sm);
}

.article-section h2 {
  font-size: 1.625rem;
  font-weight: 800;
  color: var(--slate-900);
  margin-bottom: 1rem;
}

.article-section h3 {
  font-size: 1.25rem;
  font-weight: 700;
  color: var(--slate-800);
  margin-top: 1.5rem;
  margin-bottom: 0.5rem;
}

.article-section p {
  margin-bottom: 1rem;
  color: var(--slate-700);
}

.article-section ul, .article-section ol {
  margin-bottom: 1.25rem;
  padding-left: 1.5rem;
  color: var(--slate-700);
}

.article-section li {
  margin-bottom: 0.5rem;
}

.formula-box {
  background-color: var(--slate-900);
  color: #f8fafc;
  padding: 1rem 1.5rem;
  border-radius: var(--radius-md);
  font-family: monospace;
  font-size: 1.0625rem;
  margin: 1.25rem 0;
  border-left: 4px solid var(--accent);
}

.table-wrapper {
  overflow-x: auto;
  margin: 1.5rem 0;
}

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

table th {
  background-color: var(--slate-100);
  color: var(--slate-800);
  font-weight: 700;
  text-align: left;
  padding: 0.75rem 1rem;
  border-bottom: 2px solid var(--slate-200);
}

table td {
  padding: 0.75rem 1rem;
  border-bottom: 1px solid var(--slate-200);
  color: var(--slate-700);
}

table tr:nth-child(even) td {
  background-color: var(--slate-50);
}

/* FAQ Accordion */
.faq-item {
  border-bottom: 1px solid var(--slate-200);
  padding: 1.25rem 0;
}

.faq-question {
  font-size: 1.0625rem;
  font-weight: 700;
  color: var(--slate-900);
  cursor: pointer;
  display: flex;
  justify-content: space-between;
  align-items: center;
}

.faq-answer {
  margin-top: 0.75rem;
  color: var(--slate-600);
  font-size: 0.9375rem;
}

/* Feature Grid */
.features-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(280px, 1fr));
  gap: 1.5rem;
  margin: 2rem 0;
}

.feature-card {
  background-color: var(--surface);
  border-radius: var(--radius-lg);
  border: 1px solid var(--slate-200);
  padding: 1.5rem;
  box-shadow: var(--shadow-sm);
}

.feature-icon {
  width: 44px;
  height: 44px;
  border-radius: var(--radius-md);
  background-color: var(--primary-light);
  color: var(--primary);
  display: flex;
  align-items: center;
  justify-content: center;
  font-size: 1.375rem;
  margin-bottom: 1rem;
}

.feature-card h3 {
  font-size: 1.125rem;
  font-weight: 700;
  color: var(--slate-900);
  margin-bottom: 0.5rem;
}

.feature-card p {
  color: var(--slate-600);
  font-size: 0.9375rem;
}

/* Calculators List (Hub) */
.calc-nav-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(260px, 1fr));
  gap: 1.25rem;
  margin: 2rem 0;
}

.calc-nav-card {
  background-color: var(--surface);
  border: 1.5px solid var(--slate-200);
  border-radius: var(--radius-md);
  padding: 1.25rem;
  display: block;
  color: inherit;
  transition: all 0.15s ease;
}

.calc-nav-card:hover {
  border-color: var(--primary);
  box-shadow: var(--shadow-md);
  text-decoration: none;
  transform: translateY(-2px);
}

.calc-nav-title {
  font-size: 1.0625rem;
  font-weight: 700;
  color: var(--slate-900);
  margin-bottom: 0.375rem;
  display: flex;
  align-items: center;
  gap: 0.5rem;
}

.calc-nav-desc {
  font-size: 0.875rem;
  color: var(--slate-600);
}

/* Call to Action Banner */
.cta-banner {
  background: linear-gradient(135deg, var(--slate-900) 0%, #1e3a8a 100%);
  color: #ffffff;
  border-radius: var(--radius-lg);
  padding: 3rem 2rem;
  text-align: center;
  margin: 3.5rem 0;
  box-shadow: var(--shadow-lg);
}

.cta-banner h2 {
  font-size: 2rem;
  font-weight: 800;
  margin-bottom: 0.75rem;
}

.cta-banner p {
  color: var(--slate-200);
  max-width: 600px;
  margin: 0 auto 1.75rem auto;
  font-size: 1.0625rem;
}

/* Footer */
footer {
  background-color: var(--slate-900);
  color: var(--slate-200);
  padding: 3rem 1.25rem 2rem 1.25rem;
  margin-top: 4rem;
  border-top: 1px solid var(--slate-800);
}

.footer-container {
  max-width: var(--max-w);
  margin: 0 auto;
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(200px, 1fr));
  gap: 2rem;
}

.footer-col h4 {
  color: #ffffff;
  font-size: 1rem;
  margin-bottom: 1rem;
}

.footer-col ul {
  list-style: none;
  padding: 0;
}

.footer-col li {
  margin-bottom: 0.5rem;
}

.footer-col a {
  color: var(--slate-200);
  font-size: 0.875rem;
}

.footer-col a:hover {
  color: #ffffff;
}

.footer-bottom {
  max-width: var(--max-w);
  margin: 2.5rem auto 0 auto;
  padding-top: 1.5rem;
  border-top: 1px solid var(--slate-800);
  text-align: center;
  font-size: 0.8125rem;
  color: var(--slate-500);
}

/* Responsive tweaks */
@media (max-width: 640px) {
  .hero h1 {
    font-size: 1.875rem;
  }
  .hero p {
    font-size: 1rem;
  }
  .nav-links {
    display: none;
  }
  .calc-card, .results-card, .article-section {
    padding: 1.25rem;
  }
}