/* ==========================================================================
   CFT Calculator — Main Stylesheet
   Table of Contents:
   1. CSS Variables / Design Tokens
   2. Reset & Base
   3. Typography
   4. Layout Utilities
   5. Header & Navigation
   6. Hero Section
   7. Buttons
   8. Cards (Feature / Calculator / Tool)
   9. Calculator Widget
   10. Tables
   11. FAQ Accordion
   12. Content Sections (callouts, lists)
   13. CTA Section
   14. Forms (Contact)
   15. Footer
   16. 404 Page
   17. Animations & Transitions
   18. Accessibility
   19. Responsive Breakpoints
   ========================================================================== */

/* 1. CSS Variables / Design Tokens
   ========================================================================== */
:root {
  /* Brand colors */
  --color-primary: #2563EB;
  --color-primary-dark: #1D4ED8;
  --color-primary-light: #DBEAFE;
  --color-primary-soft: #EFF6FF;

  /* Neutrals */
  --color-bg: #FFFFFF;
  --color-surface: #F8FAFC;
  --color-surface-2: #F1F5F9;
  --color-border: #E2E8F0;
  --color-text: #0F172A;
  --color-text-muted: #475569;
  --color-text-faint: #94A3B8;

  /* Semantic */
  --color-success: #16A34A;
  --color-success-bg: #F0FDF4;
  --color-warning: #D97706;
  --color-warning-bg: #FFFBEB;
  --color-danger: #DC2626;
  --color-danger-bg: #FEF2F2;

  /* Typography */
  --font-base: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Helvetica, Arial, sans-serif, "Apple Color Emoji", "Segoe UI Emoji";
  --font-display: var(--font-base);
  --font-mono: "SFMono-Regular", Consolas, "Liberation Mono", Menlo, monospace;

  /* Type scale */
  --fs-xs: 0.75rem;
  --fs-sm: 0.875rem;
  --fs-base: 1rem;
  --fs-md: 1.125rem;
  --fs-lg: 1.25rem;
  --fs-xl: 1.5rem;
  --fs-2xl: 1.875rem;
  --fs-3xl: 2.25rem;
  --fs-4xl: 2.75rem;
  --fs-5xl: 3.25rem;

  /* Spacing */
  --space-1: 0.25rem;
  --space-2: 0.5rem;
  --space-3: 0.75rem;
  --space-4: 1rem;
  --space-5: 1.5rem;
  --space-6: 2rem;
  --space-8: 3rem;
  --space-10: 4rem;
  --space-12: 5rem;
  --space-16: 7rem;

  /* Radius */
  --radius-sm: 8px;
  --radius-md: 14px;
  --radius-lg: 20px;
  --radius-full: 999px;

  /* Shadows */
  --shadow-sm: 0 1px 2px rgba(15, 23, 42, 0.06);
  --shadow-md: 0 8px 24px rgba(15, 23, 42, 0.08);
  --shadow-lg: 0 20px 48px rgba(15, 23, 42, 0.12);
  --shadow-primary: 0 12px 28px rgba(37, 99, 235, 0.25);

  /* Layout */
  --container-width: 1180px;
  --header-height: 76px;

  /* Transitions */
  --transition-fast: 150ms ease;
  --transition-base: 220ms cubic-bezier(0.4, 0, 0.2, 1);
}

/* 2. Reset & Base
   ========================================================================== */
*, *::before, *::after { box-sizing: border-box; }
html { scroll-behavior: smooth; }
@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; }
}
body, h1, h2, h3, h4, p, figure, blockquote, dl, dd, ul, ol { margin: 0; }
ul[class], ol[class] { padding: 0; list-style: none; }
img, picture, svg { display: block; max-width: 100%; }
input, button, textarea, select { font: inherit; color: inherit; }
button { cursor: pointer; }
a { color: inherit; text-decoration: none; }

body {
  font-family: var(--font-base);
  background: var(--color-bg);
  color: var(--color-text);
  line-height: 1.65;
  -webkit-font-smoothing: antialiased;
  text-rendering: optimizeLegibility;
}

main { display: block; scroll-margin-top: var(--header-height); }
section { scroll-margin-top: calc(var(--header-height) + 12px); }

/* 3. Typography
   ========================================================================== */
h1, h2, h3, h4 { font-family: var(--font-display); font-weight: 800; color: var(--color-text); line-height: 1.18; letter-spacing: -0.02em; }
h1 { font-size: var(--fs-5xl); }
h2 { font-size: var(--fs-3xl); }
h3 { font-size: var(--fs-xl); }
h4 { font-size: var(--fs-md); }
p { color: var(--color-text-muted); font-size: var(--fs-base); }
.lede { font-size: var(--fs-lg); color: var(--color-text-muted); }
.eyebrow {
  display: inline-flex; align-items: center; gap: var(--space-2);
  font-size: var(--fs-xs); font-weight: 700; letter-spacing: 0.08em; text-transform: uppercase;
  color: var(--color-primary); background: var(--color-primary-soft);
  padding: var(--space-2) var(--space-4); border-radius: var(--radius-full);
}
.section-head { max-width: 720px; margin: 0 auto var(--space-8); text-align: center; }
.section-head h2 { margin-top: var(--space-3); }
.section-head p { margin-top: var(--space-3); }
a.link-inline { color: var(--color-primary); font-weight: 600; border-bottom: 1px solid transparent; transition: border-color var(--transition-fast); }
a.link-inline:hover { border-color: var(--color-primary); }

/* 4. Layout Utilities
   ========================================================================== */
.container { width: 100%; max-width: var(--container-width); margin-inline: auto; padding-inline: var(--space-5); }
.section { padding-block: var(--space-12); }
.section--tight { padding-block: var(--space-8); }
.section--alt { background: var(--color-surface); }
.grid { display: grid; gap: var(--space-6); }
.grid-2 { grid-template-columns: repeat(2, 1fr); }
.grid-3 { grid-template-columns: repeat(3, 1fr); }
.grid-4 { grid-template-columns: repeat(4, 1fr); }
.flex { display: flex; }
.flex-center { display: flex; align-items: center; justify-content: center; }
.flex-between { display: flex; align-items: center; justify-content: space-between; }
.gap-2 { gap: var(--space-2); } .gap-3 { gap: var(--space-3); } .gap-4 { gap: var(--space-4); }
.visually-hidden { position: absolute; width: 1px; height: 1px; padding: 0; margin: -1px; overflow: hidden; clip: rect(0,0,0,0); white-space: nowrap; border: 0; }
.skip-link {
  position: absolute; left: -9999px; top: 0; background: var(--color-primary); color: #fff;
  padding: var(--space-3) var(--space-5); z-index: 200; border-radius: 0 0 var(--radius-sm) 0;
}
.skip-link:focus { left: 0; }

/* 5. Header & Navigation
   ========================================================================== */
.site-header {
  position: sticky; top: 0; z-index: 100; height: var(--header-height);
  background: rgba(255,255,255,0.85); backdrop-filter: saturate(180%) blur(12px);
  border-bottom: 1px solid var(--color-border);
}
.site-header .container { height: 100%; display: flex; align-items: center; justify-content: space-between; }
.brand { display: flex; align-items: center; gap: var(--space-3); font-weight: 800; font-size: var(--fs-lg); color: var(--color-text); }
.brand-mark {
  width: 40px; height: 40px; border-radius: var(--radius-sm);
  background: linear-gradient(135deg, var(--color-primary), var(--color-primary-dark));
  display: flex; align-items: center; justify-content: center; box-shadow: var(--shadow-primary);
}
.brand-mark svg { width: 22px; height: 22px; }

.main-nav { display: flex; align-items: center; gap: var(--space-8); }
.nav-links { display: flex; align-items: center; gap: var(--space-6); }
.nav-links a {
  font-weight: 600; font-size: var(--fs-sm); color: var(--color-text-muted);
  padding: var(--space-2) 0; position: relative; transition: color var(--transition-fast);
}
.nav-links a::after {
  content: ""; position: absolute; left: 0; right: 0; bottom: -4px; height: 2px;
  background: var(--color-primary); transform: scaleX(0); transform-origin: left; transition: transform var(--transition-base);
}
.nav-links a:hover, .nav-links a[aria-current="page"] { color: var(--color-text); }
.nav-links a:hover::after, .nav-links a[aria-current="page"]::after { transform: scaleX(1); }

.header-actions { display: flex; align-items: center; gap: var(--space-4); }
.nav-toggle {
  display: none; flex-direction: column; gap: 5px; background: none; border: none; padding: var(--space-2);
}
.nav-toggle span { width: 22px; height: 2px; background: var(--color-text); border-radius: 2px; transition: var(--transition-base); }
.nav-toggle[aria-expanded="true"] span:nth-child(1) { transform: translateY(7px) rotate(45deg); }
.nav-toggle[aria-expanded="true"] span:nth-child(2) { opacity: 0; }
.nav-toggle[aria-expanded="true"] span:nth-child(3) { transform: translateY(-7px) rotate(-45deg); }

/* 6. Hero Section
   ========================================================================== */
.hero { position: relative; padding-block: var(--space-12) var(--space-10); overflow: hidden; }
.hero::before {
  content: ""; position: absolute; inset: -20% -10% auto -10%; height: 480px;
  background: radial-gradient(60% 60% at 50% 0%, var(--color-primary-soft) 0%, rgba(255,255,255,0) 70%);
  z-index: -1;
}
.hero-grid { display: grid; grid-template-columns: 1.1fr 0.9fr; gap: var(--space-10); align-items: center; }
.hero h1 { margin-top: var(--space-4); }
.hero .lede { margin-top: var(--space-4); max-width: 540px; }
.hero-actions { display: flex; gap: var(--space-4); margin-top: var(--space-6); flex-wrap: wrap; }
.hero-stats { display: flex; gap: var(--space-8); margin-top: var(--space-8); }
.hero-stats div strong { display: block; font-size: var(--fs-2xl); color: var(--color-text); font-weight: 800; }
.hero-stats div span { font-size: var(--fs-sm); color: var(--color-text-faint); }

.hero-visual { position: relative; display: flex; align-items: center; justify-content: center; }
.cube-wire { width: 100%; max-width: 380px; }

.page-hero { padding-block: var(--space-10) var(--space-8); text-align: center; }
.page-hero .container { max-width: 820px; }
.breadcrumbs { display: flex; justify-content: center; gap: var(--space-2); font-size: var(--fs-sm); color: var(--color-text-faint); margin-bottom: var(--space-4); flex-wrap: wrap; }
.breadcrumbs a { color: var(--color-text-muted); font-weight: 600; }
.breadcrumbs a:hover { color: var(--color-primary); }
.page-hero h1 { margin-top: var(--space-3); }
.page-hero .lede { margin: var(--space-4) auto 0; max-width: 640px; }

/* 7. Buttons
   ========================================================================== */
.btn {
  display: inline-flex; align-items: center; justify-content: center; gap: var(--space-2);
  font-weight: 700; font-size: var(--fs-sm); padding: var(--space-3) var(--space-6);
  border-radius: var(--radius-full); border: 1px solid transparent; transition: all var(--transition-base);
  white-space: nowrap;
}
.btn-primary { background: var(--color-primary); color: #fff; box-shadow: var(--shadow-primary); }
.btn-primary:hover { background: var(--color-primary-dark); transform: translateY(-2px); box-shadow: 0 16px 32px rgba(37,99,235,0.32); }
.btn-secondary { background: #fff; color: var(--color-text); border-color: var(--color-border); }
.btn-secondary:hover { border-color: var(--color-primary); color: var(--color-primary); transform: translateY(-2px); }
.btn-ghost { background: transparent; color: var(--color-primary); }
.btn-ghost:hover { background: var(--color-primary-soft); }
.btn-block { width: 100%; }
.btn-sm { padding: var(--space-2) var(--space-4); font-size: var(--fs-xs); }
.btn:focus-visible, a:focus-visible, input:focus-visible, button:focus-visible, select:focus-visible, textarea:focus-visible {
  outline: 3px solid var(--color-primary-light); outline-offset: 2px; border-radius: var(--radius-sm);
}

/* 8. Cards
   ========================================================================== */
.card {
  background: #fff; border: 1px solid var(--color-border); border-radius: var(--radius-lg);
  box-shadow: var(--shadow-sm); transition: transform var(--transition-base), box-shadow var(--transition-base);
}
.feature-card { padding: var(--space-6); }
.feature-card:hover { transform: translateY(-4px); box-shadow: var(--shadow-md); }
.feature-icon {
  width: 52px; height: 52px; border-radius: var(--radius-md); background: var(--color-primary-soft);
  display: flex; align-items: center; justify-content: center; margin-bottom: var(--space-4);
}
.feature-icon svg { width: 26px; height: 26px; color: var(--color-primary); }
.feature-card h3 { margin-bottom: var(--space-2); }

.tool-card {
  padding: var(--space-8); display: flex; flex-direction: column; gap: var(--space-4); position: relative; overflow: hidden;
}
.tool-card:hover { transform: translateY(-6px); box-shadow: var(--shadow-lg); border-color: var(--color-primary-light); }
.tool-card .feature-icon { width: 60px; height: 60px; }
.tool-card .feature-icon svg { width: 30px; height: 30px; }
.tool-card ul { display: flex; flex-direction: column; gap: var(--space-2); margin: var(--space-2) 0; }
.tool-card ul li { display: flex; align-items: center; gap: var(--space-2); font-size: var(--fs-sm); color: var(--color-text-muted); }
.tool-card ul li svg { width: 16px; height: 16px; color: var(--color-success); flex-shrink: 0; }

.step-card { padding: var(--space-5); text-align: left; }
.step-num {
  width: 36px; height: 36px; border-radius: var(--radius-full); background: var(--color-text);
  color: #fff; display: flex; align-items: center; justify-content: center; font-weight: 800; font-size: var(--fs-sm);
  margin-bottom: var(--space-3);
}

/* 9. Calculator Widget
   ========================================================================== */
.calculator-card {
  background: #fff; border: 1px solid var(--color-border); border-radius: var(--radius-lg);
  box-shadow: var(--shadow-lg); padding: var(--space-8); max-width: 640px; margin-inline: auto;
}
.calculator-card .calc-title { display: flex; align-items: center; gap: var(--space-3); margin-bottom: var(--space-6); }
.calc-title .feature-icon { margin-bottom: 0; }
.calc-fields { display: grid; grid-template-columns: 1fr 1fr; gap: var(--space-4); margin-bottom: var(--space-5); }
.field { display: flex; flex-direction: column; gap: var(--space-2); }
.field label { font-size: var(--fs-sm); font-weight: 700; color: var(--color-text); }
.field input, .field select {
  border: 1.5px solid var(--color-border); border-radius: var(--radius-sm); padding: var(--space-3) var(--space-4);
  font-size: var(--fs-base); background: var(--color-surface); transition: border-color var(--transition-fast), background var(--transition-fast);
}
.field input:focus, .field select:focus { border-color: var(--color-primary); background: #fff; outline: none; }
.field input.is-invalid { border-color: var(--color-danger); background: var(--color-danger-bg); }
.field-error { font-size: var(--fs-xs); color: var(--color-danger); min-height: 1em; }
.unit-select { grid-column: 1 / -1; }
.calc-actions { display: flex; gap: var(--space-3); margin-bottom: var(--space-6); flex-wrap: wrap; }

.calc-result {
  background: var(--color-primary-soft); border: 1px dashed var(--color-primary-light);
  border-radius: var(--radius-md); padding: var(--space-6); text-align: center; margin-bottom: var(--space-5);
}
.calc-result .result-label { font-size: var(--fs-sm); font-weight: 700; color: var(--color-primary); text-transform: uppercase; letter-spacing: 0.06em; }
.calc-result .result-value { font-size: var(--fs-4xl); font-weight: 800; color: var(--color-text); margin-top: var(--space-2); }
.calc-result .result-value span.unit { font-size: var(--fs-lg); color: var(--color-text-muted); font-weight: 600; margin-left: var(--space-2); }
.result-actions { display: flex; gap: var(--space-3); justify-content: center; margin-top: var(--space-4); flex-wrap: wrap; }

.conversion-list { display: grid; grid-template-columns: repeat(2, 1fr); gap: var(--space-3); }
.conversion-item {
  background: var(--color-surface); border-radius: var(--radius-sm); padding: var(--space-3) var(--space-4);
  display: flex; justify-content: space-between; align-items: center; font-size: var(--fs-sm);
}
.conversion-item .conv-label { color: var(--color-text-muted); }
.conversion-item .conv-value { font-weight: 700; color: var(--color-text); }

.calc-status[role="alert"] { font-size: var(--fs-sm); margin-top: var(--space-3); }
.calc-status.success { color: var(--color-success); }
.calc-status.error { color: var(--color-danger); }

/* 10. Tables
   ========================================================================== */
.table-wrap { overflow-x: auto; border-radius: var(--radius-md); border: 1px solid var(--color-border); }
table { width: 100%; border-collapse: collapse; font-size: var(--fs-sm); min-width: 480px; }
thead th {
  background: var(--color-surface-2); text-align: left; padding: var(--space-3) var(--space-4);
  font-weight: 700; color: var(--color-text); border-bottom: 1px solid var(--color-border);
}
tbody td { padding: var(--space-3) var(--space-4); border-bottom: 1px solid var(--color-border); color: var(--color-text-muted); }
tbody tr:last-child td { border-bottom: none; }
tbody tr:hover { background: var(--color-surface); }
caption { caption-side: top; text-align: left; font-weight: 700; padding-bottom: var(--space-3); }

/* 11. FAQ Accordion
   ========================================================================== */
.faq-list { display: flex; flex-direction: column; gap: var(--space-3); max-width: 820px; margin-inline: auto; }
.faq-item { background: #fff; border: 1px solid var(--color-border); border-radius: var(--radius-md); overflow: hidden; }
.faq-question {
  width: 100%; display: flex; justify-content: space-between; align-items: center; gap: var(--space-4);
  padding: var(--space-5); background: none; border: none; text-align: left; font-weight: 700; font-size: var(--fs-base);
}
.faq-question svg { flex-shrink: 0; width: 20px; height: 20px; color: var(--color-primary); transition: transform var(--transition-base); }
.faq-question[aria-expanded="true"] svg { transform: rotate(180deg); }
.faq-answer { max-height: 0; overflow: hidden; transition: max-height var(--transition-base), padding var(--transition-base); padding: 0 var(--space-5); }
.faq-answer p { padding-bottom: var(--space-5); }
.faq-item.is-open .faq-answer { max-height: 600px; }

/* 12. Content Sections
   ========================================================================== */
.prose { max-width: 820px; margin-inline: auto; }
.prose h2 { margin-top: var(--space-10); margin-bottom: var(--space-4); }
.prose h3 { margin-top: var(--space-8); margin-bottom: var(--space-3); }
.prose p { margin-bottom: var(--space-4); }
.prose ul, .prose ol { margin: 0 0 var(--space-4); padding-left: var(--space-6); color: var(--color-text-muted); }
.prose ul { list-style: disc; }
.prose ol { list-style: decimal; }
.prose li { margin-bottom: var(--space-2); }
.prose .table-wrap { margin: var(--space-6) 0; }

.callout {
  border-radius: var(--radius-md); padding: var(--space-5); margin: var(--space-6) 0;
  border-left: 4px solid var(--color-primary); background: var(--color-primary-soft); display: flex; gap: var(--space-3);
}
.callout svg { width: 22px; height: 22px; color: var(--color-primary); flex-shrink: 0; }
.callout p { color: var(--color-text); margin: 0; }
.callout--warning { border-color: var(--color-warning); background: var(--color-warning-bg); }
.callout--warning svg { color: var(--color-warning); }
.callout--success { border-color: var(--color-success); background: var(--color-success-bg); }
.callout--success svg { color: var(--color-success); }

.formula-box {
  background: var(--color-text); color: #fff; border-radius: var(--radius-md);
  padding: var(--space-6); text-align: center; margin: var(--space-6) 0; font-family: var(--font-mono);
}
.formula-box .formula { font-size: var(--fs-xl); font-weight: 700; }
.formula-box .formula-note { font-size: var(--fs-xs); color: var(--color-text-faint); margin-top: var(--space-2); font-family: var(--font-base); }

.example-box { background: var(--color-surface); border-radius: var(--radius-md); padding: var(--space-5); margin: var(--space-5) 0; }
.example-box h4 { margin-bottom: var(--space-2); color: var(--color-primary); }

.icon-list { display: grid; gap: var(--space-3); }
.icon-list li { display: flex; align-items: flex-start; gap: var(--space-3); color: var(--color-text-muted); }
.icon-list li svg { width: 20px; height: 20px; color: var(--color-success); flex-shrink: 0; margin-top: 3px; }

.tag-grid { display: flex; flex-wrap: wrap; gap: var(--space-3); }
.tag-pill {
  background: var(--color-surface); border: 1px solid var(--color-border); border-radius: var(--radius-full);
  padding: var(--space-2) var(--space-5); font-size: var(--fs-sm); font-weight: 600; color: var(--color-text-muted);
  display: flex; align-items: center; gap: var(--space-2);
}

/* 13. CTA Section
   ========================================================================== */
.cta-section {
  background: linear-gradient(135deg, var(--color-primary), var(--color-primary-dark));
  border-radius: var(--radius-lg); padding: var(--space-10); text-align: center; color: #fff;
}
.cta-section h2 { color: #fff; }
.cta-section p { color: rgba(255,255,255,0.85); max-width: 560px; margin: var(--space-3) auto var(--space-6); }
.cta-section .btn-primary { background: #fff; color: var(--color-primary); box-shadow: none; }
.cta-section .btn-primary:hover { background: var(--color-surface); }
.related-tool {
  display: flex; align-items: center; justify-content: space-between; gap: var(--space-6); flex-wrap: wrap;
  background: var(--color-surface); border-radius: var(--radius-lg); padding: var(--space-8); border: 1px solid var(--color-border);
}

/* 14. Forms (Contact)
   ========================================================================== */
.contact-grid { display: grid; grid-template-columns: 1fr 1fr; gap: var(--space-10); align-items: start; }
.contact-form { display: flex; flex-direction: column; gap: var(--space-4); }
.contact-form textarea { resize: vertical; min-height: 140px; }
.contact-info-card { display: flex; flex-direction: column; gap: var(--space-5); }
.contact-info-item { display: flex; gap: var(--space-3); align-items: flex-start; }
.contact-info-item .feature-icon { margin-bottom: 0; flex-shrink: 0; width: 44px; height: 44px; }
.contact-info-item .feature-icon svg { width: 22px; height: 22px; }
.map-placeholder {
  width: 100%; height: 220px; border-radius: var(--radius-md); background: var(--color-surface);
  border: 1px dashed var(--color-border); display: flex; align-items: center; justify-content: center;
  color: var(--color-text-faint); font-size: var(--fs-sm); flex-direction: column; gap: var(--space-2);
}
.form-success {
  display: none; background: var(--color-success-bg); color: var(--color-success); border-radius: var(--radius-md);
  padding: var(--space-4); font-weight: 600; align-items: center; gap: var(--space-2);
}
.form-success.is-visible { display: flex; }

/* 15. Footer
   ========================================================================== */
.site-footer { background: var(--color-text); color: rgba(255,255,255,0.7); padding-top: var(--space-12); }
.footer-grid { display: grid; grid-template-columns: 1.4fr 1fr 1fr 1fr; gap: var(--space-8); padding-bottom: var(--space-10); }
.footer-brand .brand { color: #fff; }
.footer-brand p { color: rgba(255,255,255,0.55); margin-top: var(--space-4); max-width: 280px; }
.footer-col h4 { color: #fff; margin-bottom: var(--space-4); font-size: var(--fs-sm); text-transform: uppercase; letter-spacing: 0.06em; }
.footer-col ul { display: flex; flex-direction: column; gap: var(--space-3); }
.footer-col a { color: rgba(255,255,255,0.65); font-size: var(--fs-sm); transition: color var(--transition-fast); }
.footer-col a:hover { color: #fff; }
.footer-social { display: flex; gap: var(--space-3); margin-top: var(--space-5); }
.footer-social a {
  width: 38px; height: 38px; border-radius: var(--radius-full); background: rgba(255,255,255,0.08);
  display: flex; align-items: center; justify-content: center; transition: background var(--transition-fast);
}
.footer-social a:hover { background: var(--color-primary); }
.footer-social svg { width: 18px; height: 18px; color: #fff; }
.footer-bottom {
  border-top: 1px solid rgba(255,255,255,0.1); padding-block: var(--space-5);
  display: flex; justify-content: space-between; align-items: center; flex-wrap: wrap; gap: var(--space-3);
  font-size: var(--fs-xs); color: rgba(255,255,255,0.45);
}
.footer-bottom a { color: rgba(255,255,255,0.55); }
.footer-bottom a:hover { color: #fff; }

/* 15b. Author Box (premium trust-building component)
   ========================================================================== */
.author-box {
  position: relative; overflow: hidden; background: #fff; border: 1px solid var(--color-border);
  border-radius: 20px; box-shadow: var(--shadow-md); padding: var(--space-8);
  background-image: radial-gradient(circle at 1px 1px, rgba(37,99,235,0.05) 1px, transparent 0);
  background-size: 22px 22px;
}
.author-box::before {
  content: ""; position: absolute; top: 0; left: 0; right: 0; height: 5px;
  background: linear-gradient(90deg, var(--color-primary), #60A5FA, var(--color-primary));
}
.author-box-header {
  display: flex; align-items: center; gap: var(--space-6); flex-wrap: wrap;
  padding-bottom: var(--space-6); margin-bottom: var(--space-6); border-bottom: 1px solid var(--color-border);
}
.author-figure { margin: 0; flex-shrink: 0; }
.author-figure img {
  width: 112px; height: 112px; border-radius: 50%; object-fit: cover;
  border: 3px solid #fff; box-shadow: 0 0 0 3px var(--color-primary-light), var(--shadow-sm);
  transition: transform var(--transition-base);
}
.author-box:hover .author-figure img { transform: scale(1.04); }
.author-heading { flex: 1; min-width: 220px; }
.author-heading h3 { font-size: var(--fs-xl); margin-bottom: var(--space-1); }
.author-title { color: var(--color-primary); font-weight: 700; font-size: var(--fs-sm); margin-bottom: var(--space-3); }
.author-badges { display: flex; flex-wrap: wrap; gap: var(--space-2); }
.author-badge {
  display: inline-flex; align-items: center; gap: 6px; background: var(--color-primary-soft); color: var(--color-primary-dark);
  font-size: var(--fs-xs); font-weight: 700; padding: 6px 12px; border-radius: var(--radius-full);
  border: 1px solid var(--color-primary-light); transition: background var(--transition-fast), transform var(--transition-fast);
}
.author-badge:hover { background: var(--color-primary-light); transform: translateY(-1px); }
.author-badge svg { width: 13px; height: 13px; flex-shrink: 0; }

.author-bio p { color: var(--color-text-muted); margin-bottom: var(--space-6); }

.author-stats {
  display: grid; grid-template-columns: repeat(4, 1fr); gap: var(--space-3); margin-bottom: var(--space-6);
}
.author-stat {
  background: var(--color-surface); border: 1px solid var(--color-border); border-radius: var(--radius-md);
  padding: var(--space-4); text-align: center; transition: transform var(--transition-base), box-shadow var(--transition-base), border-color var(--transition-base);
}
.author-stat:hover { transform: translateY(-3px); box-shadow: var(--shadow-sm); border-color: var(--color-primary-light); }
.author-stat strong { display: block; font-size: var(--fs-xl); font-weight: 800; color: var(--color-primary); }
.author-stat span { font-size: var(--fs-xs); color: var(--color-text-faint); font-weight: 600; }

.author-editorial {
  background: var(--color-primary-soft); border-left: 4px solid var(--color-primary); border-radius: var(--radius-md);
  padding: var(--space-5); margin-bottom: var(--space-6); display: flex; gap: var(--space-3);
}
.author-editorial svg { width: 22px; height: 22px; color: var(--color-primary); flex-shrink: 0; }
.author-editorial h4 { font-size: var(--fs-sm); margin-bottom: var(--space-1); }
.author-editorial p { font-size: var(--fs-sm); color: var(--color-text-muted); margin: 0; }

.author-footer { display: flex; align-items: center; justify-content: space-between; gap: var(--space-4); flex-wrap: wrap; }
.author-socials { display: flex; gap: var(--space-2); }
.author-socials a {
  width: 38px; height: 38px; border-radius: 50%; background: var(--color-surface); border: 1px solid var(--color-border);
  display: flex; align-items: center; justify-content: center; transition: all var(--transition-fast);
}
.author-socials a:hover { background: var(--color-primary); border-color: var(--color-primary); transform: translateY(-2px); }
.author-socials a:hover svg { color: #fff; }
.author-socials svg { width: 17px; height: 17px; color: var(--color-text-muted); }
.author-actions { display: flex; gap: var(--space-3); flex-wrap: wrap; }

@media (max-width: 720px) {
  .author-box { padding: var(--space-6); }
  .author-box-header { flex-direction: column; text-align: center; }
  .author-badges { justify-content: center; }
  .author-stats { grid-template-columns: repeat(2, 1fr); }
  .author-footer { flex-direction: column; align-items: stretch; }
  .author-actions { justify-content: stretch; }
  .author-actions .btn { flex: 1; }
}

/* 16. 404 Page
   ========================================================================== */
.error-page { min-height: 60vh; display: flex; align-items: center; justify-content: center; text-align: center; padding-block: var(--space-12); }
.error-page .container { max-width: 560px; }
.error-illustration { width: 220px; margin: 0 auto var(--space-6); }
.error-code { font-size: var(--fs-5xl); font-weight: 800; color: var(--color-primary); }

/* 17. Animations
   ========================================================================== */
@keyframes float { 0%, 100% { transform: translateY(0); } 50% { transform: translateY(-10px); } }
.float { animation: float 5s ease-in-out infinite; }
@keyframes fadeUp { from { opacity: 0; transform: translateY(16px); } to { opacity: 1; transform: translateY(0); } }
.fade-up { animation: fadeUp 0.6s ease both; }

/* 18. Accessibility */
::selection { background: var(--color-primary-light); color: var(--color-text); }

/* 19. Responsive Breakpoints
   ========================================================================== */
@media (max-width: 1024px) {
  .hero-grid { grid-template-columns: 1fr; text-align: center; }
  .hero .lede { margin-inline: auto; }
  .hero-actions, .hero-stats { justify-content: center; }
  .hero-visual { order: -1; max-width: 320px; margin-inline: auto; }
  .footer-grid { grid-template-columns: 1fr 1fr; }
  .grid-4 { grid-template-columns: repeat(2, 1fr); }
  .grid-3 { grid-template-columns: repeat(2, 1fr); }
}

@media (max-width: 860px) {
  .main-nav { position: fixed; inset: var(--header-height) 0 0 0; background: #fff; flex-direction: column;
    align-items: stretch; padding: var(--space-6) var(--space-5); transform: translateX(100%);
    transition: transform var(--transition-base); overflow-y: auto; }
  .main-nav.is-open { transform: translateX(0); }
  .nav-links { flex-direction: column; align-items: flex-start; gap: var(--space-5); }
  .header-actions .btn-primary { display: none; }
  .main-nav .btn-primary { display: inline-flex; margin-top: var(--space-6); }
  .nav-toggle { display: flex; }
  .contact-grid { grid-template-columns: 1fr; }
}

@media (max-width: 720px) {
  :root { --fs-5xl: 2.4rem; --fs-4xl: 2.1rem; --fs-3xl: 1.7rem; }
  .grid-2, .grid-3, .grid-4 { grid-template-columns: 1fr; }
  .calc-fields { grid-template-columns: 1fr; }
  .conversion-list { grid-template-columns: 1fr; }
  .footer-grid { grid-template-columns: 1fr; gap: var(--space-6); }
  .related-tool { flex-direction: column; text-align: center; }
  .section { padding-block: var(--space-8); }
}

@media (max-width: 480px) {
  .container { padding-inline: var(--space-4); }
  .calculator-card { padding: var(--space-5); }
  .hero-stats { flex-wrap: wrap; gap: var(--space-5); }
}

/* Print */
@media print {
  .site-header, .site-footer, .nav-toggle, .hero-actions, .calc-actions, .result-actions { display: none; }
}