:root {
  --color-white: #FFFFFF;
  --color-primary: #1A73E8;
  --color-primary-dark: #1557B0;
  --color-primary-light: #E8F0FE;
  --color-text: #202124;
  --color-text-secondary: #5F6368;
  --color-bg-light: #F1F3F4;
  --color-border: #E8EAED;
  --color-success: #0F9D58;
  --color-success-light: #E6F4EA;
  --color-error: #EA4335;
  --font-stack: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Oxygen, Ubuntu, Cantarell, "Fira Sans", "Droid Sans", "Helvetica Neue", sans-serif;
  --radius-sm: 4px;
  --radius-md: 8px;
  --radius-lg: 24px;
  --radius-full: 50%;
  --shadow-1: 0 1px 2px 0 rgba(60,64,67,0.3), 0 1px 3px 1px rgba(60,64,67,0.15);
  --header-height: 56px;
  --transition-speed: 300ms;
}

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

html {
  scroll-behavior: smooth;
  -webkit-text-size-adjust: 100%;
}

@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 {
  font-family: var(--font-stack);
  font-size: 16px;
  line-height: 1.6;
  color: var(--color-text);
  background-color: var(--color-white);
  -webkit-font-smoothing: antialiased;
  min-height: 100vh;
  display: flex;
  flex-direction: column;
}

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

/* Screen reader only utility */
.sr-only {
  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
   ============================================================ */
.skip-link {
  position: absolute;
  top: -100%;
  left: 16px;
  z-index: 1000;
  padding: 8px 16px;
  background-color: var(--color-primary);
  color: #fff;
  font-size: 14px;
  font-weight: 500;
  border-radius: var(--radius-sm);
  text-decoration: none;
  transition: top 150ms ease;
}
.skip-link:focus {
  top: 8px;
}

/* ============================================================
   HEADER
   ============================================================ */
#site-header {
  position: fixed;
  top: 0; left: 0; right: 0;
  height: var(--header-height);
  background-color: var(--color-white);
  border-bottom: 1px solid var(--color-border);
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: 0 16px;
  z-index: 100;
}

.header-logo {
  display: flex;
  align-items: center;
  gap: 10px;
  text-decoration: none;
  color: var(--color-text);
  font-size: clamp(13px, 3.5vw, 18px);
  font-weight: 500;
  letter-spacing: -0.2px;
  white-space: nowrap;
}

.header-back {
  font-size: 14px;
  font-weight: 500;
  color: var(--color-primary);
  text-decoration: none;
  padding: 6px 12px;
  border-radius: var(--radius-sm);
  transition: background-color 200ms ease;
}
.header-back:hover {
  background-color: var(--color-primary-light);
}

/* ============================================================
   MAIN & HERO
   ============================================================ */
#main-content {
  flex: 1;
  margin-top: var(--header-height);
}

.page-hero {
  background-color: var(--color-primary-light);
  border-bottom: 1px solid var(--color-border);
  padding: 40px 16px 32px;
  text-align: center;
}
.page-hero h1 {
  font-size: clamp(24px, 5vw, 36px);
  font-weight: 400;
  color: var(--color-text);
  letter-spacing: -0.5px;
  margin-bottom: 8px;
}
.page-hero p {
  font-size: 16px;
  color: var(--color-text-secondary);
  max-width: 560px;
  margin: 0 auto;
}
.page-hero .last-updated {
  font-size: 13px;
  color: var(--color-text-secondary);
}

/* ============================================================
   CONTENT STYLING
   ============================================================ */
.page-content {
  max-width: 720px;
  margin: 0 auto;
  padding: 40px 16px 64px;
}

.page-content h2 {
  font-size: 20px;
  font-weight: 500;
  color: var(--color-text);
  margin: 36px 0 10px;
  border-bottom: 1px solid var(--color-border);
  padding-bottom: 8px;
}
.page-content h2:first-child {
  margin-top: 0;
}
.page-content h3 {
  font-size: 17px;
  font-weight: 500;
  color: var(--color-text);
  margin: 20px 0 6px;
}
.page-content p {
  font-size: 16px;
  color: var(--color-text-secondary);
  line-height: 1.7;
  margin-bottom: 14px;
}
.page-content ul, .page-content ol {
  margin: 0 0 16px 22px;
}
.page-content li {
  font-size: 16px;
  color: var(--color-text-secondary);
  line-height: 1.7;
  margin-bottom: 8px;
}
.page-content li strong {
  color: var(--color-text);
}

/* Callout Box */
.callout {
  background-color: var(--color-primary-light);
  border-left: 4px solid var(--color-primary);
  border-radius: var(--radius-md);
  padding: 16px 20px;
  margin: 20px 0;
}
.callout p {
  color: var(--color-text);
  margin: 0;
}

/* Warning Callout Box */
.warning-callout {
  background-color: #FDF4F2;
  border-left: 4px solid var(--color-error);
  border-radius: var(--radius-md);
  padding: 16px 20px;
  margin: 20px 0;
}
.warning-callout p {
  color: var(--color-text);
  margin: 0;
}


/* ============================================================
   ABOUT SPECIFIC STYLES
   ============================================================ */
.feature-grid {
  display: grid;
  grid-template-columns: 1fr;
  gap: 12px;
  margin: 20px 0;
}
.feature-card {
  background-color: var(--color-white);
  border: 1px solid var(--color-border);
  border-radius: var(--radius-md);
  padding: 20px;
  box-shadow: var(--shadow-1);
}
.feature-card .icon {
  font-size: 28px;
  margin-bottom: 10px;
}
.feature-card h3 {
  font-size: 16px;
  font-weight: 500;
  color: var(--color-text);
  margin-bottom: 6px;
}
.feature-card p {
  font-size: 14px;
  color: var(--color-text-secondary);
  line-height: 1.6;
  margin: 0;
}

.equation-block {
  background-color: var(--color-bg-light);
  border: 1px solid var(--color-border);
  border-radius: var(--radius-md);
  padding: 20px;
  margin: 20px 0;
  font-size: 15px;
  color: var(--color-text);
}
.equation-block .eq-label {
  font-weight: 500;
  margin-bottom: 8px;
}
.equation-block .eq-formula {
  font-family: "Courier New", monospace;
  background-color: var(--color-white);
  border: 1px solid var(--color-border);
  border-radius: var(--radius-sm);
  padding: 10px 14px;
  font-size: 14px;
  line-height: 1.8;
  overflow-x: auto;
  display: block;
}

.cta-section {
  background-color: var(--color-primary-light);
  border-radius: var(--radius-md);
  padding: 28px 24px;
  text-align: center;
  margin: 32px 0 0;
}
.cta-section p {
  color: var(--color-text);
  margin-bottom: 16px;
  font-size: 16px;
}
.btn-cta {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  height: 48px;
  padding: 0 32px;
  font-size: 15px;
  font-weight: 500;
  font-family: var(--font-stack);
  color: var(--color-white);
  background-color: var(--color-primary);
  border: none;
  border-radius: var(--radius-lg);
  cursor: pointer;
  text-decoration: none;
  transition: background-color 200ms ease;
}
.btn-cta:hover {
  background-color: var(--color-primary-dark);
  color: var(--color-white);
}

/* ============================================================
   CONTACT SPECIFIC STYLES
   ============================================================ */
.contact-layout {
  max-width: 900px;
  margin: 0 auto;
  padding: 40px 16px 64px;
  display: grid;
  grid-template-columns: 1fr;
  gap: 40px;
}

.contact-info h2 {
  font-size: 20px;
  font-weight: 500;
  color: var(--color-text);
  margin-bottom: 14px;
  border-bottom: 1px solid var(--color-border);
  padding-bottom: 8px;
}
.contact-info p {
  font-size: 15px;
  color: var(--color-text-secondary);
  line-height: 1.7;
  margin-bottom: 14px;
}

.contact-card {
  display: flex;
  align-items: flex-start;
  gap: 14px;
  background-color: var(--color-white);
  border: 1px solid var(--color-border);
  border-radius: var(--radius-md);
  padding: 18px 20px;
  margin-bottom: 12px;
  box-shadow: var(--shadow-1);
}
.contact-card .icon {
  font-size: 24px;
  flex-shrink: 0;
  padding-top: 2px;
}
.contact-card .label {
  font-size: 13px;
  font-weight: 500;
  color: var(--color-text-secondary);
  text-transform: uppercase;
  letter-spacing: 0.5px;
  margin-bottom: 4px;
}
.contact-card .value {
  font-size: 15px;
  color: var(--color-text);
}
.contact-card a {
  color: var(--color-primary);
  text-decoration: none;
}
.contact-card a:hover {
  color: var(--color-primary-dark);
  text-decoration: underline;
}

.response-note {
  background-color: var(--color-bg-light);
  border-radius: var(--radius-md);
  padding: 14px 16px;
  margin-top: 8px;
  font-size: 14px;
  color: var(--color-text-secondary);
  line-height: 1.6;
}

.contact-form-wrap h2 {
  font-size: 20px;
  font-weight: 500;
  color: var(--color-text);
  margin-bottom: 14px;
  border-bottom: 1px solid var(--color-border);
  padding-bottom: 8px;
}

.form-group {
  display: flex;
  flex-direction: column;
  margin-bottom: 18px;
}
.form-group label {
  font-size: 14px;
  font-weight: 500;
  color: var(--color-text);
  margin-bottom: 6px;
}
.form-group input, .form-group select, .form-group textarea {
  font-family: var(--font-stack);
  font-size: 16px;
  color: var(--color-text);
  background-color: var(--color-white);
  border: 1px solid var(--color-border);
  border-radius: var(--radius-sm);
  padding: 10px 12px;
  width: 100%;
  transition: border-color 200ms ease, box-shadow 200ms ease;
}
.form-group input:focus, .form-group select:focus, .form-group textarea:focus {
  border-color: var(--color-primary);
  box-shadow: 0 0 0 2px var(--color-primary-light);
  outline: none;
}
.form-group textarea {
  resize: vertical;
  min-height: 140px;
  line-height: 1.6;
}

.btn-submit {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  height: 48px;
  padding: 0 32px;
  font-size: 15px;
  font-weight: 500;
  font-family: var(--font-stack);
  color: var(--color-white);
  background-color: var(--color-primary);
  border: none;
  border-radius: var(--radius-lg);
  cursor: pointer;
  transition: background-color 200ms ease;
  width: 100%;
}
.btn-submit:hover {
  background-color: var(--color-primary-dark);
}

.form-success {
  display: none;
  background-color: var(--color-success-light);
  border: 1px solid var(--color-success);
  border-radius: var(--radius-md);
  padding: 14px 16px;
  font-size: 15px;
  color: var(--color-success);
  margin-top: 14px;
}
.form-success.visible {
  display: block;
}

/* FAQ / Details accordion styling */
.faq-section {
  margin-top: 24px;
}
.faq-section h2 {
  font-size: 20px;
  font-weight: 500;
  color: var(--color-text);
  margin-bottom: 14px;
  border-bottom: 1px solid var(--color-border);
  padding-bottom: 8px;
}
details {
  border: 1px solid var(--color-border);
  border-radius: var(--radius-md);
  margin-bottom: 8px;
  background-color: var(--color-white);
  overflow: hidden;
}
summary {
  padding: 14px 16px;
  font-size: 15px;
  font-weight: 500;
  color: var(--color-text);
  cursor: pointer;
  list-style: none;
  display: flex;
  justify-content: space-between;
  align-items: center;
  gap: 8px;
  transition: background-color 200ms ease;
}
summary:hover {
  background-color: var(--color-bg-light);
}
summary::-webkit-details-marker {
  display: none;
}
summary::after {
  content: '+';
  font-size: 20px;
  color: var(--color-primary);
  flex-shrink: 0;
}
details[open] summary::after {
  content: '\2212';
}
details p {
  padding: 4px 16px 14px;
  border-top: 1px solid var(--color-border);
  font-size: 15px;
  color: var(--color-text-secondary);
  line-height: 1.7;
}

/* ============================================================
   FOOTER
   ============================================================ */
#site-footer {
  background-color: var(--color-bg-light);
  border-top: 1px solid var(--color-border);
}
.footer-links {
  max-width: 680px;
  margin: 0 auto;
  padding: 32px 16px 24px;
  display: flex;
  flex-wrap: wrap;
  gap: 8px 24px;
  justify-content: center;
}
.footer-links a {
  color: var(--color-text-secondary);
  text-decoration: none;
  font-size: 14px;
  padding: 4px 0;
  transition: color 200ms ease;
}
.footer-links a:hover {
  color: var(--color-primary);
}
.footer-bottom {
  border-top: 1px solid var(--color-border);
  padding: 16px;
  text-align: center;
}
.footer-bottom p {
  font-size: 13px;
  color: var(--color-text-secondary);
}
.footer-bottom .site-name {
  font-weight: 500;
  color: var(--color-text);
}

/* ============================================================
   RESPONSIVE DESIGN
   ============================================================ */
@media (min-width: 600px) {
  .page-hero {
    padding: 56px 24px 40px;
  }
  .page-content {
    padding: 48px 24px 80px;
  }
  .feature-grid {
    grid-template-columns: 1fr 1fr;
  }
}
@media (min-width: 768px) {
  .contact-layout {
    grid-template-columns: 1fr 1fr;
    align-items: start;
  }
}
@media (min-width: 1024px) {
  #site-header {
    padding: 0 32px;
  }
  .page-hero {
    padding: 64px 32px 48px;
  }
  .page-content {
    padding: 56px 32px 96px;
  }
  .feature-grid {
    grid-template-columns: 1fr 1fr 1fr;
  }
  .contact-layout {
    padding: 56px 32px 96px;
    max-width: 960px;
  }
}

/* ============================================================
   SCROLL TO TOP BUTTON
   ============================================================ */
.scroll-to-top-btn {
  position: fixed;
  bottom: 24px;
  right: 24px;
  width: 48px;
  height: 48px;
  border-radius: var(--radius-full);
  background-color: var(--color-primary);
  color: var(--color-white);
  border: none;
  cursor: pointer;
  box-shadow: var(--shadow-1);
  display: flex;
  align-items: center;
  justify-content: center;
  opacity: 0;
  visibility: hidden;
  pointer-events: none;
  transform: translateY(10px);
  transition: opacity 300ms ease, transform 300ms ease, background-color 200ms ease, box-shadow 200ms ease;
  z-index: 99;
}
.scroll-to-top-btn.visible {
  opacity: 1;
  visibility: visible;
  pointer-events: auto;
  transform: translateY(0);
}
.scroll-to-top-btn:hover {
  background-color: var(--color-primary-dark);
  box-shadow: var(--shadow-1);
  transform: scale(1.05);
}
.scroll-to-top-btn:active {
  transform: scale(0.95);
}
.scroll-to-top-btn:focus-visible {
  outline: 2px solid var(--color-primary-dark);
  outline-offset: 2px;
  background-color: var(--color-primary-dark);
}
@media print {
  .scroll-to-top-btn { display: none !important; }
}

/* Inline form validation error styling */
.error-msg {
  color: var(--color-error);
  font-size: 13px;
  margin-top: 4px;
  display: none;
}
.error-msg.visible {
  display: block;
}