/* ==========================================================================
   AIO Calculator — Core Design System & CSS
   Mobile-First, High Contrast, Zero Layout Shift, Accessible
   ========================================================================== */

:root {
  --color-primary: #1d4ed8;
  --color-primary-hover: #1e40af;
  --color-primary-light: #eff6ff;
  --color-primary-border: #bfdbfe;
  
  --color-success: #047857;
  --color-success-light: #ecfdf5;
  --color-warning: #b45309;
  --color-warning-light: #fffbeb;
  --color-danger: #be123c;
  --color-danger-light: #fff1f2;

  --color-slate-900: #0f172a;
  --color-slate-800: #1e293b;
  --color-slate-700: #334155;
  --color-slate-600: #475569;
  --color-slate-500: #64748b;
  --color-slate-400: #94a3b8;
  --color-slate-300: #cbd5e1;
  --color-slate-200: #e2e8f0;
  --color-slate-100: #f1f5f9;
  --color-slate-50: #f8fafc;
  --color-white: #ffffff;

  --font-sans: system-ui, -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, Oxygen, Ubuntu, Cantarell, sans-serif;
  --font-mono: ui-monospace, SFMono-Regular, Menlo, Monaco, Consolas, monospace;

  --shadow-sm: 0 1px 2px 0 rgba(0, 0, 0, 0.05);
  --shadow-md: 0 4px 6px -1px rgba(0, 0, 0, 0.08), 0 2px 4px -2px rgba(0, 0, 0, 0.06);
  --shadow-lg: 0 10px 15px -3px rgba(0, 0, 0, 0.08), 0 4px 6px -4px rgba(0, 0, 0, 0.04);
  --shadow-card: 0 2px 8px rgba(15, 23, 42, 0.06);

  --radius-sm: 6px;
  --radius-md: 10px;
  --radius-lg: 16px;
  --radius-full: 9999px;

  --max-w-content: 1200px;
  --max-w-prose: 760px;
  --header-height: 68px;
}

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

html {
  font-family: var(--font-sans);
  font-size: 16px;
  line-height: 1.6;
  color: var(--color-slate-800);
  background-color: var(--color-slate-50);
  scroll-behavior: smooth;
  -webkit-text-size-adjust: 100%;
}

body {
  min-height: 100vh;
  display: flex;
  flex-direction: column;
}

a {
  color: var(--color-primary);
  text-decoration: underline;
  text-decoration-thickness: 1px;
  text-underline-offset: 3px;
  transition: color 0.15s ease;
}

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

h1, h2, h3, h4, h5, h6 {
  color: var(--color-slate-900);
  font-weight: 700;
  line-height: 1.25;
}

h1 {
  font-size: 2.25rem;
  letter-spacing: -0.025em;
  margin-bottom: 0.75rem;
}

h2 {
  font-size: 1.5rem;
  margin-top: 2rem;
  margin-bottom: 0.75rem;
  letter-spacing: -0.02em;
}

h3 {
  font-size: 1.2rem;
  margin-top: 1.5rem;
  margin-bottom: 0.5rem;
}

p {
  margin-bottom: 1rem;
}

ul, ol {
  margin-bottom: 1.25rem;
  padding-left: 1.5rem;
}

li {
  margin-bottom: 0.35rem;
}

/* Layout Utilities */
.container {
  width: 100%;
  max-width: var(--max-w-content);
  margin-left: auto;
  margin-right: auto;
  padding-left: 1.25rem;
  padding-right: 1.25rem;
}

.prose {
  max-width: var(--max-w-prose);
}

/* Header & Navigation */
.site-header {
  position: sticky;
  top: 0;
  z-index: 50;
  background-color: rgba(255, 255, 255, 0.95);
  backdrop-filter: blur(8px);
  border-bottom: 1px solid var(--color-slate-200);
  height: var(--header-height);
  display: flex;
  align-items: center;
}

.header-inner {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 1.5rem;
}

.brand-link {
  display: flex;
  align-items: center;
  gap: 0.5rem;
  text-decoration: none;
  font-size: 1.35rem;
  font-weight: 800;
  color: var(--color-slate-900);
  letter-spacing: -0.03em;
}

.brand-badge {
  background-color: var(--color-primary);
  color: var(--color-white);
  font-size: 0.7rem;
  font-weight: 700;
  padding: 0.15rem 0.45rem;
  border-radius: var(--radius-sm);
  text-transform: uppercase;
}

.nav-desktop {
  display: none;
  align-items: center;
  gap: 1.25rem;
}

@media (min-width: 900px) {
  .nav-desktop {
    display: flex;
  }
}

.nav-link {
  text-decoration: none;
  color: var(--color-slate-700);
  font-weight: 600;
  font-size: 0.95rem;
  padding: 0.4rem 0.6rem;
  border-radius: var(--radius-sm);
  transition: all 0.15s ease;
}

.nav-link:hover {
  color: var(--color-primary);
  background-color: var(--color-primary-light);
}

.header-actions {
  display: flex;
  align-items: center;
  gap: 0.75rem;
}

.btn-search-trigger {
  display: flex;
  align-items: center;
  gap: 0.5rem;
  background-color: var(--color-slate-100);
  border: 1px solid var(--color-slate-300);
  color: var(--color-slate-600);
  padding: 0.45rem 0.9rem;
  border-radius: var(--radius-full);
  font-size: 0.9rem;
  cursor: pointer;
  transition: all 0.15s ease;
}

.btn-search-trigger:hover {
  border-color: var(--color-primary);
  color: var(--color-primary);
  background-color: var(--color-white);
}

/* Trust Banner Strip */
.trust-strip {
  background-color: var(--color-white);
  border-bottom: 1px solid var(--color-slate-200);
  padding: 0.75rem 0;
  font-size: 0.85rem;
  color: var(--color-slate-600);
}

.trust-strip-inner {
  display: flex;
  flex-wrap: wrap;
  align-items: center;
  justify-content: center;
  gap: 1.5rem;
  text-align: center;
}

.trust-item {
  display: inline-flex;
  align-items: center;
  gap: 0.35rem;
  font-weight: 500;
}

.trust-icon {
  color: var(--color-success);
}

/* Breadcrumbs */
.breadcrumbs {
  padding: 0.85rem 0;
  font-size: 0.85rem;
  color: var(--color-slate-500);
}

.breadcrumbs ol {
  display: flex;
  flex-wrap: wrap;
  align-items: center;
  list-style: none;
  padding: 0;
  margin: 0;
  gap: 0.4rem;
}

.breadcrumbs li + li::before {
  content: "/";
  margin-right: 0.4rem;
  color: var(--color-slate-400);
}

.breadcrumbs a {
  color: var(--color-slate-600);
  text-decoration: none;
}

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

/* Main Content Two-Column Grid for Tool Pages */
.tool-page-grid {
  display: grid;
  grid-template-columns: 1fr;
  gap: 2.5rem;
  margin-top: 1.5rem;
  margin-bottom: 3.5rem;
}

@media (min-width: 960px) {
  .tool-page-grid {
    grid-template-columns: minmax(0, 1fr) 300px;
  }
}

/* Calculator Card Styles */
.calculator-card {
  background-color: var(--color-white);
  border: 1px solid var(--color-slate-200);
  border-radius: var(--radius-lg);
  box-shadow: var(--shadow-card);
  padding: 1.5rem;
  margin-bottom: 2rem;
}

@media (min-width: 640px) {
  .calculator-card {
    padding: 2rem;
  }
}

.calculator-card-header {
  border-bottom: 1px solid var(--color-slate-100);
  padding-bottom: 1rem;
  margin-bottom: 1.5rem;
}

.calc-grid {
  display: grid;
  grid-template-columns: 1fr;
  gap: 1.75rem;
}

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

/* Form Controls */
.form-group {
  margin-bottom: 1.25rem;
}

.form-label {
  display: flex;
  align-items: center;
  justify-content: space-between;
  font-weight: 600;
  font-size: 0.95rem;
  color: var(--color-slate-900);
  margin-bottom: 0.45rem;
}

.form-label-hint {
  font-size: 0.8rem;
  font-weight: 400;
  color: var(--color-slate-500);
}

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

.input-prefix, .input-suffix {
  position: absolute;
  color: var(--color-slate-500);
  font-size: 0.95rem;
  pointer-events: none;
  font-weight: 500;
}

.input-prefix {
  left: 0.85rem;
}

.input-suffix {
  right: 0.85rem;
}

.form-input, .form-select {
  width: 100%;
  min-height: 48px; /* Standard 48px Mobile Accessibility touch target */
  padding: 0.65rem 0.85rem;
  font-size: 1rem;
  font-family: inherit;
  color: var(--color-slate-900);
  background-color: var(--color-white);
  border: 1.5px solid var(--color-slate-300);
  border-radius: var(--radius-md);
  transition: all 0.15s ease;
}

.form-input.has-prefix {
  padding-left: 2rem;
}

.form-input.has-suffix {
  padding-right: 2.75rem;
}

.form-input:focus, .form-select:focus {
  outline: none;
  border-color: var(--color-primary);
  box-shadow: 0 0 0 3px rgba(29, 78, 216, 0.15);
}

.form-range {
  width: 100%;
  margin-top: 0.5rem;
  accent-color: var(--color-primary);
  cursor: pointer;
}

/* Results Display Box (Strictly Zero Layout Shift: Pre-allocated height) */
.results-box {
  background: linear-gradient(135deg, #f8fafc 0%, #eff6ff 100%);
  border: 1.5px solid var(--color-primary-border);
  border-radius: var(--radius-md);
  padding: 1.25rem;
  display: flex;
  flex-direction: column;
  justify-content: space-between;
}

.result-main {
  text-align: center;
  padding: 0.75rem 0;
}

.result-label {
  font-size: 0.85rem;
  font-weight: 600;
  text-transform: uppercase;
  letter-spacing: 0.05em;
  color: var(--color-slate-600);
  margin-bottom: 0.35rem;
}

.result-value {
  font-size: 2.25rem;
  font-weight: 800;
  color: var(--color-primary);
  line-height: 1.1;
  font-variant-numeric: tabular-nums;
}

.result-breakdown {
  margin-top: 1rem;
  border-top: 1px solid rgba(29, 78, 216, 0.12);
  padding-top: 0.75rem;
  font-size: 0.9rem;
}

.breakdown-row {
  display: flex;
  justify-content: space-between;
  padding: 0.35rem 0;
  color: var(--color-slate-700);
}

.breakdown-row.highlight {
  font-weight: 700;
  color: var(--color-slate-900);
}

.result-actions {
  display: flex;
  gap: 0.5rem;
  margin-top: 1rem;
}

.btn {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  gap: 0.5rem;
  min-height: 48px; /* Standard 48px Mobile Accessibility touch target */
  padding: 0.6rem 1.2rem;
  border-radius: var(--radius-md);
  font-size: 0.95rem;
  font-weight: 600;
  cursor: pointer;
  border: 1px solid transparent;
  text-decoration: none;
  transition: all 0.15s ease;
}

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

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

.btn-secondary {
  background-color: var(--color-white);
  border-color: var(--color-slate-300);
  color: var(--color-slate-700);
}

.btn-secondary:hover {
  border-color: var(--color-slate-400);
  background-color: var(--color-slate-100);
}

.btn-sm {
  min-height: 36px;
  padding: 0.35rem 0.75rem;
  font-size: 0.85rem;
}

/* Mathematical Formula Box */
.math-formula {
  background-color: var(--color-white);
  border: 1px solid var(--color-slate-200);
  border-left: 4px solid var(--color-primary);
  padding: 1rem 1.25rem;
  border-radius: var(--radius-sm);
  margin: 1.25rem 0;
  overflow-x: auto;
}

.math-formula code {
  font-family: var(--font-mono);
  font-size: 0.95rem;
  color: var(--color-slate-900);
  font-weight: 600;
}

/* Worked Example Card */
.example-card {
  background-color: var(--color-white);
  border: 1px solid var(--color-slate-200);
  border-radius: var(--radius-md);
  padding: 1.25rem;
  margin: 1.25rem 0;
}

.example-card-header {
  font-weight: 700;
  color: var(--color-slate-900);
  margin-bottom: 0.75rem;
  display: flex;
  align-items: center;
  gap: 0.5rem;
}

.example-result-pill {
  display: inline-block;
  background-color: var(--color-success-light);
  color: var(--color-success);
  font-weight: 700;
  padding: 0.4rem 0.75rem;
  border-radius: var(--radius-sm);
  margin-top: 0.75rem;
}

/* Alert Boxes */
.alert-box {
  padding: 1rem 1.25rem;
  border-radius: var(--radius-md);
  margin: 1.25rem 0;
  font-size: 0.925rem;
}

.alert-warning {
  background-color: var(--color-warning-light);
  border-left: 4px solid var(--color-warning);
  color: #78350f;
}

.alert-info {
  background-color: var(--color-primary-light);
  border-left: 4px solid var(--color-primary);
  color: #1e3a8a;
}

/* FAQs */
.faq-section {
  margin-top: 2.5rem;
}

.faq-item {
  background-color: var(--color-white);
  border: 1px solid var(--color-slate-200);
  border-radius: var(--radius-md);
  margin-bottom: 0.85rem;
  overflow: hidden;
}

.faq-question {
  width: 100%;
  text-align: left;
  padding: 1.1rem 1.25rem;
  font-size: 1.05rem;
  font-weight: 600;
  color: var(--color-slate-900);
  background: none;
  border: none;
  cursor: pointer;
  display: flex;
  justify-content: space-between;
  align-items: center;
}

.faq-answer {
  padding: 0 1.25rem 1.1rem;
  color: var(--color-slate-700);
  font-size: 0.95rem;
  line-height: 1.6;
}

/* Source & Date line */
.source-line {
  margin-top: 2rem;
  padding-top: 1rem;
  border-top: 1px solid var(--color-slate-200);
  font-size: 0.825rem;
  color: var(--color-slate-500);
}

/* Sidebar Navigation */
.sidebar {
  position: sticky;
  top: calc(var(--header-height) + 1.5rem);
}

.sidebar-card {
  background-color: var(--color-white);
  border: 1px solid var(--color-slate-200);
  border-radius: var(--radius-lg);
  padding: 1.25rem;
  margin-bottom: 1.5rem;
}

.sidebar-title {
  font-size: 1rem;
  font-weight: 700;
  color: var(--color-slate-900);
  margin-bottom: 0.85rem;
  padding-bottom: 0.5rem;
  border-bottom: 1px solid var(--color-slate-100);
}

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

.sidebar-item {
  margin-bottom: 0.35rem;
}

.sidebar-link {
  display: block;
  padding: 0.45rem 0.65rem;
  border-radius: var(--radius-sm);
  color: var(--color-slate-700);
  text-decoration: none;
  font-size: 0.9rem;
  font-weight: 500;
  transition: all 0.15s ease;
}

.sidebar-link:hover {
  background-color: var(--color-slate-100);
  color: var(--color-primary);
}

.sidebar-link.active {
  background-color: var(--color-primary-light);
  color: var(--color-primary);
  font-weight: 700;
}

/* Hub Tabs */
.hub-nav {
  display: flex;
  flex-wrap: wrap;
  gap: 0.5rem;
  margin-bottom: 1.5rem;
  border-bottom: 2px solid var(--color-slate-200);
  padding-bottom: 0.5rem;
}

.hub-tab-btn {
  padding: 0.6rem 1rem;
  border-radius: var(--radius-md) var(--radius-md) 0 0;
  background-color: var(--color-slate-100);
  border: 1px solid var(--color-slate-200);
  border-bottom: none;
  font-weight: 600;
  font-size: 0.95rem;
  color: var(--color-slate-700);
  cursor: pointer;
  text-decoration: none;
}

.hub-tab-btn:hover {
  background-color: var(--color-white);
  color: var(--color-primary);
}

.hub-tab-btn.active {
  background-color: var(--color-primary);
  color: var(--color-white);
  border-color: var(--color-primary);
}

.hub-panel {
  display: block;
  margin-bottom: 2rem;
}

/* Tables */
.table-responsive {
  overflow-x: auto;
  margin: 1.25rem 0;
}

table {
  width: 100%;
  border-collapse: collapse;
  text-align: left;
  font-size: 0.925rem;
  background-color: var(--color-white);
  border-radius: var(--radius-md);
  overflow: hidden;
  border: 1px solid var(--color-slate-200);
}

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

th {
  background-color: var(--color-slate-100);
  font-weight: 700;
  color: var(--color-slate-900);
}

/* Footer */
.site-footer {
  margin-top: auto;
  background-color: var(--color-slate-900);
  color: var(--color-slate-300);
  padding: 3.5rem 0 2rem;
  font-size: 0.9rem;
}

.footer-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(200px, 1fr));
  gap: 2.5rem;
  margin-bottom: 2.5rem;
}

.footer-col h4 {
  color: var(--color-white);
  font-size: 1rem;
  margin-bottom: 1rem;
}

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

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

.footer-col a {
  color: var(--color-slate-400);
  text-decoration: none;
  transition: color 0.15s ease;
}

.footer-col a:hover {
  color: var(--color-white);
}

.footer-bottom {
  border-top: 1px solid var(--color-slate-800);
  padding-top: 1.5rem;
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: space-between;
  gap: 1rem;
  font-size: 0.85rem;
  color: var(--color-slate-500);
}

@media (min-width: 640px) {
  .footer-bottom {
    flex-direction: row;
  }
}

/* Search Modal */
.search-modal-backdrop {
  position: fixed;
  inset: 0;
  background-color: rgba(15, 23, 42, 0.6);
  backdrop-filter: blur(4px);
  z-index: 100;
  display: none;
  align-items: flex-start;
  justify-content: center;
  padding: 4rem 1rem 1rem;
}

.search-modal-backdrop.open {
  display: flex;
}

.search-modal {
  width: 100%;
  max-width: 640px;
  background-color: var(--color-white);
  border-radius: var(--radius-lg);
  box-shadow: var(--shadow-lg);
  overflow: hidden;
}

.search-header {
  padding: 1rem 1.25rem;
  border-bottom: 1px solid var(--color-slate-200);
  display: flex;
  align-items: center;
  gap: 0.75rem;
}

.search-input {
  width: 100%;
  border: none;
  font-size: 1.15rem;
  outline: none;
  font-family: inherit;
}

.search-results {
  max-height: 400px;
  overflow-y: auto;
  padding: 0.5rem;
}

.search-result-item {
  display: block;
  padding: 0.75rem 1rem;
  border-radius: var(--radius-md);
  text-decoration: none;
  color: var(--color-slate-800);
  transition: background 0.15s ease;
}

.search-result-item:hover, .search-result-item.highlighted {
  background-color: var(--color-primary-light);
}

.search-result-title {
  font-weight: 700;
  color: var(--color-slate-900);
  display: flex;
  align-items: center;
  justify-content: space-between;
}

.search-result-cat {
  font-size: 0.75rem;
  background-color: var(--color-slate-100);
  padding: 0.15rem 0.45rem;
  border-radius: var(--radius-sm);
  color: var(--color-slate-600);
}

.search-result-desc {
  font-size: 0.85rem;
  color: var(--color-slate-600);
  margin-top: 0.25rem;
}

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