/* =============================================================================
   AdaptiveLMS — Design System
   CSS Custom Properties (Design Tokens)
   ============================================================================= */

/* -----------------------------------------------------------------------------
   1. Color Palette
   ----------------------------------------------------------------------------- */
:root {
  /* Primary — deep blue */
  --color-primary-50:  #eff6ff;
  --color-primary-100: #dbeafe;
  --color-primary-200: #bfdbfe;
  --color-primary-300: #93c5fd;
  --color-primary-400: #60a5fa;
  --color-primary-500: #3b82f6;
  --color-primary-600: #2563eb;
  --color-primary-700: #1d4ed8;
  --color-primary-800: #1e40af;
  --color-primary-900: #1e3a8a;

  /* Secondary — purple */
  --color-secondary-50:  #faf5ff;
  --color-secondary-100: #f3e8ff;
  --color-secondary-200: #e9d5ff;
  --color-secondary-300: #d8b4fe;
  --color-secondary-400: #c084fc;
  --color-secondary-500: #a855f7;
  --color-secondary-600: #9333ea;
  --color-secondary-700: #7e22ce;
  --color-secondary-800: #6b21a8;
  --color-secondary-900: #581c87;

  /* Accent — teal */
  --color-accent-50:  #f0fdfa;
  --color-accent-100: #ccfbf1;
  --color-accent-200: #99f6e4;
  --color-accent-300: #5eead4;
  --color-accent-400: #2dd4bf;
  --color-accent-500: #14b8a6;
  --color-accent-600: #0d9488;
  --color-accent-700: #0f766e;
  --color-accent-800: #115e59;
  --color-accent-900: #134e4a;

  /* Neutral — slate */
  --color-neutral-0:   #ffffff;
  --color-neutral-50:  #f8fafc;
  --color-neutral-100: #f1f5f9;
  --color-neutral-200: #e2e8f0;
  --color-neutral-300: #cbd5e1;
  --color-neutral-400: #94a3b8;
  --color-neutral-500: #64748b;
  --color-neutral-600: #475569;
  --color-neutral-700: #334155;
  --color-neutral-800: #1e293b;
  --color-neutral-900: #0f172a;
  --color-neutral-950: #020617;

  /* Semantic color aliases */
  --color-bg:           var(--color-neutral-950);
  --color-bg-surface:   var(--color-neutral-900);
  --color-bg-elevated:  var(--color-neutral-800);
  --color-text:         var(--color-neutral-50);
  --color-text-muted:   var(--color-neutral-400);
  --color-text-subtle:  var(--color-neutral-500);
  --color-border:       var(--color-neutral-800);
  --color-border-muted: var(--color-neutral-700);

  /* Brand gradient */
  --gradient-brand: linear-gradient(135deg, var(--color-primary-600), var(--color-secondary-600));
  --gradient-hero:  linear-gradient(135deg, #0f172a 0%, #1e1b4b 50%, #0f172a 100%);
  --gradient-card:  linear-gradient(135deg, var(--color-neutral-900), var(--color-neutral-800));

  /* Focus ring */
  --color-focus: var(--color-primary-400);
}

/* -----------------------------------------------------------------------------
   2. Typography Scale
   ----------------------------------------------------------------------------- */
:root {
  /* Font families */
  --font-sans: 'Inter', system-ui, -apple-system, BlinkMacSystemFont, 'Segoe UI', sans-serif;
  --font-mono: 'JetBrains Mono', 'Fira Code', 'Cascadia Code', monospace;

  /* Font sizes — fluid type scale (clamp: min, preferred, max) */
  --text-xs:   clamp(0.694rem, 0.65rem + 0.22vw,  0.75rem);   /* 11–12px */
  --text-sm:   clamp(0.833rem, 0.79rem + 0.22vw,  0.875rem);  /* 13–14px */
  --text-base: clamp(1rem,     0.96rem + 0.22vw,  1rem);      /* 16px */
  --text-lg:   clamp(1.125rem, 1.05rem + 0.38vw,  1.25rem);   /* 18–20px */
  --text-xl:   clamp(1.25rem,  1.15rem + 0.5vw,   1.5rem);    /* 20–24px */
  --text-2xl:  clamp(1.5rem,   1.35rem + 0.75vw,  2rem);      /* 24–32px */
  --text-3xl:  clamp(1.875rem, 1.6rem + 1.38vw,   2.5rem);    /* 30–40px */
  --text-4xl:  clamp(2.25rem,  1.85rem + 2vw,     3.5rem);    /* 36–56px */
  --text-5xl:  clamp(3rem,     2.4rem + 3vw,      4.5rem);    /* 48–72px */

  /* Font weights */
  --font-light:    300;
  --font-regular:  400;
  --font-medium:   500;
  --font-semibold: 600;
  --font-bold:     700;
  --font-extrabold: 800;

  /* Line heights */
  --leading-none:    1;
  --leading-tight:   1.25;
  --leading-snug:    1.375;
  --leading-normal:  1.5;
  --leading-relaxed: 1.625;
  --leading-loose:   2;

  /* Letter spacing */
  --tracking-tight:  -0.025em;
  --tracking-normal:  0em;
  --tracking-wide:    0.025em;
  --tracking-wider:   0.05em;
  --tracking-widest:  0.1em;
}

/* -----------------------------------------------------------------------------
   3. Spacing Scale (4px base unit)
   ----------------------------------------------------------------------------- */
:root {
  --space-0:    0;
  --space-px:   1px;
  --space-0-5:  0.125rem;  /* 2px */
  --space-1:    0.25rem;   /* 4px */
  --space-1-5:  0.375rem;  /* 6px */
  --space-2:    0.5rem;    /* 8px */
  --space-2-5:  0.625rem;  /* 10px */
  --space-3:    0.75rem;   /* 12px */
  --space-3-5:  0.875rem;  /* 14px */
  --space-4:    1rem;      /* 16px */
  --space-5:    1.25rem;   /* 20px */
  --space-6:    1.5rem;    /* 24px */
  --space-7:    1.75rem;   /* 28px */
  --space-8:    2rem;      /* 32px */
  --space-9:    2.25rem;   /* 36px */
  --space-10:   2.5rem;    /* 40px */
  --space-11:   2.75rem;   /* 44px */
  --space-12:   3rem;      /* 48px */
  --space-14:   3.5rem;    /* 56px */
  --space-16:   4rem;      /* 64px */
  --space-20:   5rem;      /* 80px */
  --space-24:   6rem;      /* 96px */
  --space-28:   7rem;      /* 112px */
  --space-32:   8rem;      /* 128px */
  --space-36:   9rem;      /* 144px */
  --space-40:   10rem;     /* 160px */
  --space-48:   12rem;     /* 192px */
  --space-56:   14rem;     /* 224px */
  --space-64:   16rem;     /* 256px */

  /* Section padding */
  --section-padding-y: clamp(var(--space-16), 8vw, var(--space-32));
  --section-padding-x: clamp(var(--space-4),  5vw, var(--space-16));

  /* Container max-width */
  --container-sm:  640px;
  --container-md:  768px;
  --container-lg:  1024px;
  --container-xl:  1280px;
  --container-2xl: 1536px;
}

/* -----------------------------------------------------------------------------
   4. Breakpoints (reference only — used in media queries below)
   ----------------------------------------------------------------------------- */
/*
  --bp-sm:  640px
  --bp-md:  768px
  --bp-lg:  1024px
  --bp-xl:  1280px
  --bp-2xl: 1536px
*/

/* -----------------------------------------------------------------------------
   5. Border Radius & Shadows
   ----------------------------------------------------------------------------- */
:root {
  --radius-sm:   0.25rem;   /* 4px */
  --radius-md:   0.5rem;    /* 8px */
  --radius-lg:   0.75rem;   /* 12px */
  --radius-xl:   1rem;      /* 16px */
  --radius-2xl:  1.5rem;    /* 24px */
  --radius-full: 9999px;

  --shadow-sm:  0 1px 2px 0 rgb(0 0 0 / 0.3);
  --shadow-md:  0 4px 6px -1px rgb(0 0 0 / 0.4), 0 2px 4px -2px rgb(0 0 0 / 0.3);
  --shadow-lg:  0 10px 15px -3px rgb(0 0 0 / 0.5), 0 4px 6px -4px rgb(0 0 0 / 0.3);
  --shadow-xl:  0 20px 25px -5px rgb(0 0 0 / 0.5), 0 8px 10px -6px rgb(0 0 0 / 0.3);
  --shadow-glow-primary:   0 0 20px rgb(59 130 246 / 0.3);
  --shadow-glow-secondary: 0 0 20px rgb(168 85 247 / 0.3);
  --shadow-glow-accent:    0 0 20px rgb(20 184 166 / 0.3);
}

/* -----------------------------------------------------------------------------
   6. Transitions & Animations
   ----------------------------------------------------------------------------- */
:root {
  --duration-fast:   150ms;
  --duration-normal: 250ms;
  --duration-slow:   400ms;
  --duration-slower: 600ms;

  --ease-default:    cubic-bezier(0.4, 0, 0.2, 1);
  --ease-in:         cubic-bezier(0.4, 0, 1, 1);
  --ease-out:        cubic-bezier(0, 0, 0.2, 1);
  --ease-in-out:     cubic-bezier(0.4, 0, 0.2, 1);
  --ease-bounce:     cubic-bezier(0.34, 1.56, 0.64, 1);

  --transition-base:     all var(--duration-normal) var(--ease-default);
  --transition-colors:   color var(--duration-fast) var(--ease-default),
                         background-color var(--duration-fast) var(--ease-default),
                         border-color var(--duration-fast) var(--ease-default);
  --transition-transform: transform var(--duration-normal) var(--ease-out);
  --transition-opacity:   opacity var(--duration-normal) var(--ease-default);
}

/* =============================================================================
   7. CSS Reset & Base Styles
   ============================================================================= */

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

html {
  scroll-behavior: smooth;
  font-size: 100%; /* 16px base */
  -webkit-text-size-adjust: 100%;
  tab-size: 4;
}

body {
  font-family: var(--font-sans);
  font-size: var(--text-base);
  font-weight: var(--font-regular);
  line-height: var(--leading-normal);
  color: var(--color-text);
  background-color: var(--color-bg);
  -webkit-font-smoothing: antialiased;
  -moz-osx-font-smoothing: grayscale;
  overflow-x: hidden;
}

/* Improve media defaults */
img,
picture,
video,
canvas,
svg {
  display: block;
  max-width: 100%;
}

/* Inherit fonts for form elements */
input,
button,
textarea,
select {
  font: inherit;
}

/* Avoid text overflows */
p,
h1,
h2,
h3,
h4,
h5,
h6 {
  overflow-wrap: break-word;
}

/* Remove list styles on ul/ol with role="list" */
ul[role='list'],
ol[role='list'] {
  list-style: none;
}

/* Focus styles */
:focus-visible {
  outline: 2px solid var(--color-focus);
  outline-offset: 3px;
  border-radius: var(--radius-sm);
}

/* Skip to main content link (accessibility) */
.skip-link {
  position: absolute;
  top: -100%;
  left: var(--space-4);
  padding: var(--space-2) var(--space-4);
  background: var(--color-primary-600);
  color: var(--color-neutral-0);
  font-weight: var(--font-semibold);
  border-radius: var(--radius-md);
  text-decoration: none;
  z-index: 9999;
  transition: top var(--duration-fast) var(--ease-out);
}

.skip-link:focus {
  top: var(--space-4);
}

/* =============================================================================
   8. Layout Utilities
   ============================================================================= */

.container {
  width: 100%;
  max-width: var(--container-xl);
  margin-inline: auto;
  padding-inline: var(--section-padding-x);
}

.section {
  padding-block: var(--section-padding-y);
}

/* =============================================================================
   9. Navigation Bar
   ============================================================================= */

.site-header {
  position: fixed;
  top: 0;
  left: 0;
  right: 0;
  z-index: 100;
  background: rgb(2 6 23 / 0.8);
  backdrop-filter: blur(12px);
  -webkit-backdrop-filter: blur(12px);
  border-bottom: 1px solid var(--color-border);
  transition: var(--transition-colors);
}

.nav {
  display: flex;
  align-items: center;
  justify-content: space-between;
  max-width: var(--container-xl);
  margin-inline: auto;
  padding-inline: var(--section-padding-x);
  height: 4rem;
  gap: var(--space-4);
}

.nav__brand {
  display: flex;
  align-items: center;
  gap: var(--space-2);
  font-size: var(--text-lg);
  font-weight: var(--font-bold);
  color: var(--color-text);
  text-decoration: none;
  letter-spacing: var(--tracking-tight);
  white-space: nowrap;
  transition: var(--transition-colors);
}

.nav__brand:hover {
  color: var(--color-primary-400);
}

.nav__brand-icon {
  font-size: var(--text-xl);
  background: var(--gradient-brand);
  -webkit-background-clip: text;
  -webkit-text-fill-color: transparent;
  background-clip: text;
}

.nav__links {
  display: flex;
  align-items: center;
  gap: var(--space-1);
  list-style: none;
}

.nav__link {
  display: inline-flex;
  align-items: center;
  padding: var(--space-2) var(--space-3);
  font-size: var(--text-sm);
  font-weight: var(--font-medium);
  color: var(--color-text-muted);
  text-decoration: none;
  border-radius: var(--radius-md);
  transition: var(--transition-colors);
  white-space: nowrap;
}

.nav__link:hover,
.nav__link.active {
  color: var(--color-text);
  background: var(--color-bg-elevated);
}

.nav__link.active {
  color: var(--color-primary-400);
}

.nav__link--cta {
  background: var(--gradient-brand);
  color: var(--color-neutral-0) !important;
  padding: var(--space-2) var(--space-4);
  font-weight: var(--font-semibold);
}

.nav__link--cta:hover {
  opacity: 0.9;
  background: var(--gradient-brand);
}

/* Hamburger button — hidden on desktop */
.nav__hamburger {
  display: none;
  align-items: center;
  justify-content: center;
  width: 2.5rem;
  height: 2.5rem;
  background: transparent;
  border: 1px solid var(--color-border);
  border-radius: var(--radius-md);
  color: var(--color-text);
  cursor: pointer;
  transition: var(--transition-colors);
}

.nav__hamburger:hover {
  background: var(--color-bg-elevated);
}

/* Mobile nav */
@media (max-width: 767px) {
  .nav__hamburger {
    display: flex;
  }

  .nav__links {
    position: absolute;
    top: 4rem;
    left: 0;
    right: 0;
    flex-direction: column;
    align-items: stretch;
    gap: 0;
    background: var(--color-bg-surface);
    border-bottom: 1px solid var(--color-border);
    padding: var(--space-2);
    max-height: 0;
    overflow: hidden;
    transition: max-height var(--duration-slow) var(--ease-out),
                padding var(--duration-slow) var(--ease-out);
  }

  .nav__links.nav-open {
    max-height: 24rem;
    padding: var(--space-2);
  }

  .nav__link {
    padding: var(--space-3) var(--space-4);
    font-size: var(--text-base);
    border-radius: var(--radius-md);
  }

  .nav__link--cta {
    margin-top: var(--space-2);
    text-align: center;
    justify-content: center;
  }
}

/* =============================================================================
   10. Section Placeholder Styles (filled in later tasks)
   ============================================================================= */

.section--hero {
  min-height: 100vh;
  display: flex;
  align-items: center;
  justify-content: center;
  background: var(--gradient-hero);
  padding-top: 4rem; /* offset fixed nav */
}

.section--problem,
.section--solution,
.section--features,
.section--technology {
  background: var(--color-bg);
}

.section--problem {
  background: var(--color-bg-surface);
}

.section--contact {
  background: var(--color-bg-surface);
}

/* =============================================================================
   11. Problem Statement Section
   ============================================================================= */

/* --- Section header (shared pattern) --- */
.section__header {
  text-align: center;
  max-width: 56ch;
  margin-inline: auto;
  margin-bottom: var(--space-16);
}

.section__title {
  font-size: var(--text-3xl);
  font-weight: var(--font-extrabold);
  line-height: var(--leading-tight);
  letter-spacing: var(--tracking-tight);
  color: var(--color-text);
  margin-bottom: var(--space-5);
}

.section__intro {
  font-size: var(--text-lg);
  line-height: var(--leading-relaxed);
  color: var(--color-text-muted);
}

/* --- Challenge cards grid --- */
.challenges-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(160px, 1fr));
  gap: var(--space-6);
}

/* --- Card base --- */
.card {
  background: var(--gradient-card);
  border: 1px solid var(--color-border);
  border-radius: var(--radius-xl);
  padding: var(--space-8);
  display: flex;
  flex-direction: column;
  gap: var(--space-4);
  transition: transform var(--duration-normal) var(--ease-out),
              box-shadow var(--duration-normal) var(--ease-out),
              border-color var(--duration-normal) var(--ease-default);
}

.card:hover {
  transform: translateY(-4px);
  box-shadow: var(--shadow-xl), var(--shadow-glow-primary);
  border-color: var(--color-border-muted);
}

/* --- Card icon --- */
.card__icon {
  display: flex;
  align-items: center;
  justify-content: center;
  width: 3rem;
  height: 3rem;
  background: rgb(59 130 246 / 0.12);
  border: 1px solid rgb(59 130 246 / 0.25);
  border-radius: var(--radius-lg);
  color: var(--color-primary-400);
  flex-shrink: 0;
}

.card__icon svg,
.card__icon i {
  width: 1.5rem;
  height: 1.5rem;
}

/* --- Card title --- */
.card__title {
  font-size: var(--text-lg);
  font-weight: var(--font-semibold);
  line-height: var(--leading-snug);
  color: var(--color-text);
}

/* --- Card description --- */
.card__description {
  font-size: var(--text-sm);
  line-height: var(--leading-relaxed);
  color: var(--color-text-muted);
  flex: 1;
}

/* --- Responsive: single column on small screens --- */
@media (max-width: 639px) {
  .challenges-grid {
    grid-template-columns: 1fr;
  }
}

/* =============================================================================
   11b. Solution / Core Concepts Section
   ============================================================================= */

/* --- Component cards grid (2-column on desktop, 1 on mobile) --- */
.components-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(480px, 1fr));
  gap: var(--space-6);
}

@media (max-width: 639px) {
  .components-grid {
    grid-template-columns: 1fr;
  }
}

/* =============================================================================
   11c. Pipeline Flow Diagram
   ============================================================================= */

.pipeline {
  display: flex;
  flex-direction: row;
  align-items: center;
  justify-content: center;
  gap: 0;
  margin-bottom: var(--space-16);
  flex-wrap: nowrap;
}

/* Individual step box */
.pipeline__step {
  position: relative;
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: center;
  gap: var(--space-2);
  padding: var(--space-5) var(--space-6);
  background: var(--gradient-card);
  border: 1px solid var(--color-border);
  border-radius: var(--radius-xl);
  min-width: 9rem;
  text-align: center;
  transition: transform var(--duration-normal) var(--ease-out),
              box-shadow var(--duration-normal) var(--ease-out),
              border-color var(--duration-normal) var(--ease-default);
}

.pipeline__step:hover {
  transform: translateY(-3px);
  box-shadow: var(--shadow-lg), var(--shadow-glow-primary);
  border-color: var(--color-primary-600);
}

/* Step number badge */
.pipeline__step-number {
  font-size: var(--text-xs);
  font-weight: var(--font-bold);
  letter-spacing: var(--tracking-wider);
  color: var(--color-primary-400);
  background: rgb(59 130 246 / 0.12);
  border: 1px solid rgb(59 130 246 / 0.25);
  border-radius: var(--radius-full);
  padding: var(--space-0-5) var(--space-2);
  line-height: 1.4;
}

/* Step label */
.pipeline__step-label {
  font-size: var(--text-sm);
  font-weight: var(--font-semibold);
  color: var(--color-text);
  line-height: var(--leading-snug);
}

/* Arrow connector — ::after pseudo-element on every step except the last */
.pipeline__step:not(.pipeline__step--last)::after {
  content: '→';
  position: absolute;
  right: calc(-1 * var(--space-6));
  top: 50%;
  transform: translateY(-50%);
  font-size: var(--text-xl);
  color: var(--color-primary-400);
  line-height: 1;
  pointer-events: none;
  z-index: 1;
}

/* Responsive: stack vertically on mobile */
@media (max-width: 767px) {
  .pipeline {
    flex-direction: column;
    align-items: center;
    gap: var(--space-8);
  }

  .pipeline__step {
    width: 100%;
    max-width: 18rem;
    flex-direction: row;
    justify-content: flex-start;
    text-align: left;
    gap: var(--space-4);
  }

  /* Down arrow on mobile */
  .pipeline__step:not(.pipeline__step--last)::after {
    content: '↓';
    right: auto;
    top: auto;
    bottom: calc(-1 * var(--space-6));
    left: 50%;
    transform: translateX(-50%);
    font-size: var(--text-xl);
  }
}

/* =============================================================================
   11d. Features Section
   ============================================================================= */

/* --- Features grid: auto-fit columns, min 260px --- */
.features-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(360px, 1fr));
  gap: var(--space-6);
}

/* --- Feature tile (card-like) --- */
.feature-tile {
  background: var(--gradient-card);
  border: 1px solid var(--color-border);
  border-radius: var(--radius-xl);
  padding: var(--space-8);
  display: flex;
  flex-direction: column;
  gap: var(--space-4);
  transition: transform var(--duration-normal) var(--ease-out),
              box-shadow var(--duration-normal) var(--ease-out),
              border-color var(--duration-normal) var(--ease-default);
}

.feature-tile:hover {
  transform: translateY(-4px);
  box-shadow: var(--shadow-xl), var(--shadow-glow-secondary);
  border-color: var(--color-secondary-700);
}

/* --- Tile icon wrapper --- */
.feature-tile__icon {
  display: flex;
  align-items: center;
  justify-content: center;
  width: 3rem;
  height: 3rem;
  background: rgb(168 85 247 / 0.12);
  border: 1px solid rgb(168 85 247 / 0.25);
  border-radius: var(--radius-lg);
  color: var(--color-secondary-400);
  flex-shrink: 0;
}

.feature-tile__icon i {
  width: 1.5rem;
  height: 1.5rem;
}

/* --- Tile title --- */
.feature-tile__title {
  font-size: var(--text-lg);
  font-weight: var(--font-semibold);
  line-height: var(--leading-snug);
  color: var(--color-text);
}

/* --- Tile description --- */
.feature-tile__description {
  font-size: var(--text-sm);
  line-height: var(--leading-relaxed);
  color: var(--color-text-muted);
  flex: 1;
}

/* --- Responsive: single column on small screens --- */
@media (max-width: 639px) {
  .features-grid {
    grid-template-columns: 1fr;
  }
}

/* =============================================================================
   11e. Technology / Impact Section
   ============================================================================= */

/* --- Metrics grid: 3 equal columns, auto-fit on smaller screens --- */
.metrics-grid {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  gap: var(--space-6);
  margin-bottom: var(--space-16);
}

@media (max-width: 767px) {
  .metrics-grid {
    grid-template-columns: 1fr;
  }
}

@media (min-width: 768px) and (max-width: 1023px) {
  .metrics-grid {
    grid-template-columns: repeat(auto-fit, minmax(220px, 1fr));
  }
}

/* --- Metric card --- */
.metric-card {
  background: var(--gradient-card);
  border: 1px solid var(--color-border);
  border-radius: var(--radius-xl);
  padding: var(--space-10) var(--space-8);
  display: flex;
  flex-direction: column;
  align-items: center;
  text-align: center;
  gap: var(--space-3);
  transition: transform var(--duration-normal) var(--ease-out),
              box-shadow var(--duration-normal) var(--ease-out),
              border-color var(--duration-normal) var(--ease-default);
}

.metric-card:hover {
  transform: translateY(-4px);
  box-shadow: var(--shadow-xl), var(--shadow-glow-accent);
  border-color: var(--color-accent-700);
}

/* --- Prefix ("Up to") --- */
.metric-card__prefix {
  font-size: var(--text-sm);
  font-weight: var(--font-medium);
  letter-spacing: var(--tracking-wide);
  text-transform: uppercase;
  color: var(--color-accent-400);
}

/* --- Numeric value + suffix wrapper --- */
.metric-card__number {
  display: flex;
  align-items: baseline;
  gap: var(--space-1);
  line-height: var(--leading-none);
}

/* --- Large numeric value --- */
.metric-card__value {
  font-size: var(--text-5xl);
  font-weight: var(--font-extrabold);
  letter-spacing: var(--tracking-tight);
  background: var(--gradient-brand);
  -webkit-background-clip: text;
  -webkit-text-fill-color: transparent;
  background-clip: text;
  line-height: var(--leading-none);
}

/* --- Suffix (%) --- */
.metric-card__suffix {
  font-size: var(--text-3xl);
  font-weight: var(--font-bold);
  color: var(--color-primary-400);
}

/* --- Label text below the number --- */
.metric-card__label {
  font-size: var(--text-base);
  font-weight: var(--font-medium);
  line-height: var(--leading-snug);
  color: var(--color-text-muted);
  max-width: 20ch;
}

/* =============================================================================
   12. Scroll-Reveal Animation Base
   ============================================================================= */

.reveal {
  opacity: 0;
  transform: translateY(20px);
  transition: opacity var(--duration-slower) var(--ease-out),
              transform var(--duration-slower) var(--ease-out);
}

.reveal.revealed {
  opacity: 1;
  transform: translateY(0);
}

/* Respect prefers-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;
    scroll-behavior: auto !important;
  }

  .reveal {
    opacity: 1;
    transform: none;
    transition: none;
  }
}

/* =============================================================================
   12. Utility Classes
   ============================================================================= */

.sr-only {
  position: absolute;
  width: 1px;
  height: 1px;
  padding: 0;
  margin: -1px;
  overflow: hidden;
  clip: rect(0, 0, 0, 0);
  white-space: nowrap;
  border-width: 0;
}

.text-gradient {
  background: var(--gradient-brand);
  -webkit-background-clip: text;
  -webkit-text-fill-color: transparent;
  background-clip: text;
}

.text-center { text-align: center; }
.text-left   { text-align: left; }
.text-right  { text-align: right; }

/* =============================================================================
   13. Hero Section
   ============================================================================= */

/* --- Animated gradient background --- */
@keyframes hero-gradient-shift {
  0%   { background-position: 0% 50%; }
  50%  { background-position: 100% 50%; }
  100% { background-position: 0% 50%; }
}

.section--hero {
  /* Override the static gradient with an animated one */
  background: linear-gradient(
    135deg,
    #0f172a 0%,
    #1e1b4b 25%,
    #0c1a3a 50%,
    #1a0a2e 75%,
    #0f172a 100%
  );
  background-size: 300% 300%;
  animation: hero-gradient-shift 12s ease infinite;
  position: relative;
  overflow: hidden;
}

/* Subtle radial glow overlay */
.section--hero::before {
  content: '';
  position: absolute;
  inset: 0;
  background:
    radial-gradient(ellipse 60% 50% at 70% 50%, rgb(59 130 246 / 0.12) 0%, transparent 70%),
    radial-gradient(ellipse 40% 60% at 20% 40%, rgb(168 85 247 / 0.10) 0%, transparent 70%);
  pointer-events: none;
}

/* --- Layout --- */
.hero__container {
  display: grid;
  grid-template-columns: 1fr 1fr;
  align-items: center;
  gap: var(--space-16);
  min-height: calc(100vh - 4rem); /* subtract nav height */
  padding-block: var(--space-20);
}

/* --- Text content --- */
.hero__eyebrow {
  display: inline-block;
  font-size: var(--text-xs);
  font-weight: var(--font-semibold);
  letter-spacing: var(--tracking-widest);
  text-transform: uppercase;
  color: var(--color-primary-400);
  background: rgb(59 130 246 / 0.12);
  border: 1px solid rgb(59 130 246 / 0.25);
  border-radius: var(--radius-full);
  padding: var(--space-1) var(--space-3);
  margin-bottom: var(--space-5);
}

.hero__headline {
  font-size: var(--text-5xl);
  font-weight: var(--font-extrabold);
  line-height: var(--leading-tight);
  letter-spacing: var(--tracking-tight);
  color: var(--color-text);
  margin-bottom: var(--space-6);
}

.hero__subheadline {
  font-size: var(--text-lg);
  font-weight: var(--font-regular);
  line-height: var(--leading-relaxed);
  color: var(--color-text-muted);
  max-width: 52ch;
  margin-bottom: var(--space-10);
}

/* --- CTA Button --- */
.btn {
  display: inline-flex;
  align-items: center;
  gap: var(--space-2);
  padding: var(--space-3-5) var(--space-7);
  font-size: var(--text-base);
  font-weight: var(--font-semibold);
  border-radius: var(--radius-full);
  text-decoration: none;
  cursor: pointer;
  border: none;
  transition: transform var(--duration-normal) var(--ease-out),
              box-shadow var(--duration-normal) var(--ease-out),
              opacity var(--duration-fast) var(--ease-default);
}

.btn--primary {
  background: var(--gradient-brand);
  color: var(--color-neutral-0);
  box-shadow: var(--shadow-glow-primary);
}

.btn--primary:hover {
  transform: translateY(-2px);
  box-shadow: 0 0 32px rgb(59 130 246 / 0.45), var(--shadow-lg);
}

.btn--primary:active {
  transform: translateY(0);
}

.btn__icon {
  flex-shrink: 0;
  transition: transform var(--duration-normal) var(--ease-bounce);
}

.btn--primary:hover .btn__icon {
  transform: translateX(4px);
}

/* --- Neural-network illustration --- */
.hero__illustration {
  display: flex;
  align-items: center;
  justify-content: center;
}

.neural-net {
  width: 100%;
  max-width: 420px;
  height: auto;
  filter: drop-shadow(0 0 24px rgb(59 130 246 / 0.2));
}

/* Edges */
.nn-edge {
  stroke: rgb(99 102 241 / 0.35);
  stroke-width: 1.5;
  stroke-linecap: round;
}

/* Nodes */
.nn-node {
  stroke-width: 2;
}

.nn-node--input {
  fill: rgb(59 130 246 / 0.25);
  stroke: var(--color-primary-400);
}

.nn-node--hidden {
  fill: rgb(168 85 247 / 0.25);
  stroke: var(--color-secondary-400);
}

.nn-node--output {
  fill: rgb(20 184 166 / 0.25);
  stroke: var(--color-accent-400);
}

/* Pulsing glow on nodes */
@keyframes nn-pulse {
  0%, 100% { opacity: 0.6; r: 14; }
  50%       { opacity: 1;   r: 17; }
}

.nn-pulse-1 { animation: nn-pulse 2.4s ease-in-out infinite; }
.nn-pulse-2 { animation: nn-pulse 2.4s ease-in-out infinite 0.8s; }
.nn-pulse-3 { animation: nn-pulse 2.4s ease-in-out infinite 1.6s; }

/* Travelling signal dots */
@keyframes nn-travel-a {
  0%   { cx: 70;  cy: 80;  opacity: 0; }
  10%  { opacity: 1; }
  45%  { cx: 200; cy: 130; opacity: 1; }
  55%  { cx: 200; cy: 130; opacity: 1; }
  90%  { cx: 330; cy: 200; opacity: 1; }
  100% { cx: 330; cy: 200; opacity: 0; }
}

@keyframes nn-travel-b {
  0%   { cx: 70;  cy: 190; opacity: 0; }
  10%  { opacity: 1; }
  45%  { cx: 200; cy: 270; opacity: 1; }
  55%  { cx: 200; cy: 270; opacity: 1; }
  90%  { cx: 330; cy: 290; opacity: 1; }
  100% { cx: 330; cy: 290; opacity: 0; }
}

@keyframes nn-travel-c {
  0%   { cx: 70;  cy: 300; opacity: 0; }
  10%  { opacity: 1; }
  45%  { cx: 200; cy: 60;  opacity: 1; }
  55%  { cx: 200; cy: 60;  opacity: 1; }
  90%  { cx: 330; cy: 110; opacity: 1; }
  100% { cx: 330; cy: 110; opacity: 0; }
}

.nn-signal--a {
  fill: var(--color-primary-400);
  animation: nn-travel-a 3s ease-in-out infinite;
}

.nn-signal--b {
  fill: var(--color-secondary-400);
  animation: nn-travel-b 3s ease-in-out infinite 1s;
}

.nn-signal--c {
  fill: var(--color-accent-400);
  animation: nn-travel-c 3s ease-in-out infinite 2s;
}

/* Layer labels */
.nn-label {
  fill: var(--color-text-subtle);
  font-family: var(--font-sans);
  font-size: 11px;
  text-anchor: middle;
  letter-spacing: 0.05em;
}

/* --- Scroll-down hint --- */
@keyframes hero-bounce {
  0%, 100% { transform: translateY(0); }
  50%       { transform: translateY(6px); }
}

.hero__scroll-hint {
  position: absolute;
  bottom: var(--space-8);
  left: 50%;
  transform: translateX(-50%);
  display: flex;
  align-items: center;
  justify-content: center;
  width: 2.5rem;
  height: 2.5rem;
  color: var(--color-text-muted);
  border: 1px solid var(--color-border-muted);
  border-radius: var(--radius-full);
  text-decoration: none;
  animation: hero-bounce 2s ease-in-out infinite;
  transition: color var(--duration-fast) var(--ease-default),
              border-color var(--duration-fast) var(--ease-default);
}

.hero__scroll-hint:hover {
  color: var(--color-primary-400);
  border-color: var(--color-primary-400);
}

/* --- Responsive: tablet and below --- */
@media (max-width: 1023px) {
  .hero__container {
    grid-template-columns: 1fr;
    text-align: center;
    gap: var(--space-12);
  }

  .hero__subheadline {
    margin-inline: auto;
  }

  .hero__illustration {
    order: -1; /* illustration above text on tablet */
  }

  .neural-net {
    max-width: 320px;
  }
}

@media (max-width: 767px) {
  .hero__headline {
    font-size: var(--text-4xl);
  }

  .neural-net {
    max-width: 260px;
  }
}

/* =============================================================================
   11f. Technology Section — Model Comparison Table & Validation Methodology
   ============================================================================= */

/* --- Subsection headings (shared) --- */
.subsection__title {
  font-size: var(--text-2xl);
  font-weight: var(--font-bold);
  line-height: var(--leading-tight);
  letter-spacing: var(--tracking-tight);
  color: var(--color-text);
  margin-bottom: var(--space-3);
  text-align: center;
}

.subsection__intro {
  font-size: var(--text-base);
  line-height: var(--leading-relaxed);
  color: var(--color-text-muted);
  text-align: center;
  max-width: 60ch;
  margin-inline: auto;
  margin-bottom: var(--space-8);
}

/* --- Model table wrapper --- */
.model-table-wrapper {
  margin-top: var(--space-16);
  margin-bottom: var(--space-16);
}

/* Horizontal scroll container for narrow viewports */
.model-table-scroll {
  overflow-x: auto;
  -webkit-overflow-scrolling: touch;
  border-radius: var(--radius-xl);
  border: 1px solid var(--color-border);
}

/* --- Table base --- */
.model-table {
  width: 100%;
  border-collapse: collapse;
  font-size: var(--text-sm);
  background: var(--gradient-card);
  min-width: 600px; /* prevents collapse on very small screens */
}

/* --- Table header --- */
.model-table thead tr {
  background: rgb(59 130 246 / 0.08);
  border-bottom: 1px solid var(--color-border);
}

.model-table th {
  padding: var(--space-4) var(--space-6);
  text-align: left;
  font-size: var(--text-xs);
  font-weight: var(--font-semibold);
  letter-spacing: var(--tracking-wider);
  text-transform: uppercase;
  color: var(--color-primary-400);
  white-space: nowrap;
}

/* --- Table body rows --- */
.model-table tbody tr {
  border-bottom: 1px solid var(--color-border);
  transition: background-color var(--duration-fast) var(--ease-default);
}

.model-table tbody tr:last-child {
  border-bottom: none;
}

.model-table tbody tr:hover {
  background: rgb(255 255 255 / 0.03);
}

/* --- Table cells --- */
.model-table td {
  padding: var(--space-5) var(--space-6);
  vertical-align: top;
  color: var(--color-text-muted);
  line-height: var(--leading-relaxed);
}

/* First column: model badge + name stacked */
.model-table td:first-child {
  white-space: nowrap;
  display: flex;
  flex-direction: column;
  gap: var(--space-1-5);
  min-width: 10rem;
}

/* --- Model badge chips --- */
.model-badge {
  display: inline-block;
  font-size: var(--text-xs);
  font-weight: var(--font-bold);
  letter-spacing: var(--tracking-wider);
  padding: var(--space-0-5) var(--space-2);
  border-radius: var(--radius-full);
  line-height: 1.4;
  width: fit-content;
}

.model-badge--bkt {
  background: rgb(59 130 246 / 0.15);
  border: 1px solid rgb(59 130 246 / 0.35);
  color: var(--color-primary-300);
}

.model-badge--pfa {
  background: rgb(168 85 247 / 0.15);
  border: 1px solid rgb(168 85 247 / 0.35);
  color: var(--color-secondary-300);
}

.model-badge--dkt {
  background: rgb(20 184 166 / 0.15);
  border: 1px solid rgb(20 184 166 / 0.35);
  color: var(--color-accent-300);
}

/* --- Model full name (below badge) --- */
.model-name {
  font-size: var(--text-sm);
  font-weight: var(--font-medium);
  color: var(--color-text);
  line-height: var(--leading-snug);
}

/* =============================================================================
   Validation Methodology
   ============================================================================= */

.validation-section {
  margin-bottom: var(--space-8);
}

/* --- 2×2 grid of validation cards --- */
.validation-grid {
  display: grid;
  grid-template-columns: repeat(2, 1fr);
  gap: var(--space-6);
  margin-bottom: var(--space-10);
}

@media (max-width: 639px) {
  .validation-grid {
    grid-template-columns: 1fr;
  }
}

/* --- Validation card --- */
.validation-card {
  background: var(--gradient-card);
  border: 1px solid var(--color-border);
  border-radius: var(--radius-xl);
  padding: var(--space-7) var(--space-8);
  display: flex;
  flex-direction: column;
  gap: var(--space-3);
  transition: transform var(--duration-normal) var(--ease-out),
              box-shadow var(--duration-normal) var(--ease-out),
              border-color var(--duration-normal) var(--ease-default);
}

.validation-card:hover {
  transform: translateY(-3px);
  box-shadow: var(--shadow-lg), var(--shadow-glow-primary);
  border-color: var(--color-primary-700);
}

/* --- Validation card icon --- */
.validation-card__icon {
  display: flex;
  align-items: center;
  justify-content: center;
  width: 2.75rem;
  height: 2.75rem;
  background: rgb(59 130 246 / 0.12);
  border: 1px solid rgb(59 130 246 / 0.25);
  border-radius: var(--radius-lg);
  color: var(--color-primary-400);
  flex-shrink: 0;
}

.validation-card__icon i {
  width: 1.25rem;
  height: 1.25rem;
}

/* --- Validation card title --- */
.validation-card__title {
  font-size: var(--text-base);
  font-weight: var(--font-semibold);
  color: var(--color-text);
  line-height: var(--leading-snug);
}

/* --- Validation card detail text --- */
.validation-card__detail {
  font-size: var(--text-sm);
  line-height: var(--leading-relaxed);
  color: var(--color-text-muted);
}

/* =============================================================================
   Pilot Domains
   ============================================================================= */

.pilot-domains {
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: var(--space-4);
  padding: var(--space-8);
  background: rgb(59 130 246 / 0.05);
  border: 1px solid var(--color-border);
  border-radius: var(--radius-xl);
}

.pilot-domains__label {
  font-size: var(--text-xs);
  font-weight: var(--font-semibold);
  letter-spacing: var(--tracking-wider);
  text-transform: uppercase;
  color: var(--color-text-subtle);
}

.pilot-domains__list {
  display: flex;
  flex-wrap: wrap;
  gap: var(--space-3);
  justify-content: center;
}

/* --- Pilot domain tag --- */
.pilot-tag {
  display: inline-flex;
  align-items: center;
  gap: var(--space-2);
  padding: var(--space-2) var(--space-4);
  background: var(--gradient-card);
  border: 1px solid var(--color-border-muted);
  border-radius: var(--radius-full);
  font-size: var(--text-sm);
  font-weight: var(--font-medium);
  color: var(--color-text);
  transition: border-color var(--duration-fast) var(--ease-default),
              box-shadow var(--duration-fast) var(--ease-default);
}

.pilot-tag:hover {
  border-color: var(--color-primary-600);
  box-shadow: var(--shadow-glow-primary);
}

.pilot-tag i {
  width: 1rem;
  height: 1rem;
  color: var(--color-primary-400);
  flex-shrink: 0;
}

/* =============================================================================
   14. Call-to-Action / Contact Section
   ============================================================================= */

.section--contact {
  background: linear-gradient(
    135deg,
    var(--color-neutral-950) 0%,
    #1e1b4b 50%,
    var(--color-neutral-950) 100%
  );
  position: relative;
  overflow: hidden;
}

/* Subtle radial glow overlay */
.section--contact::before {
  content: '';
  position: absolute;
  inset: 0;
  background:
    radial-gradient(ellipse 60% 60% at 50% 50%, rgb(59 130 246 / 0.10) 0%, transparent 70%),
    radial-gradient(ellipse 40% 40% at 80% 20%, rgb(168 85 247 / 0.08) 0%, transparent 70%);
  pointer-events: none;
}

.contact__container {
  position: relative;
  z-index: 1;
}

.contact__content {
  display: flex;
  flex-direction: column;
  align-items: center;
  text-align: center;
  gap: var(--space-8);
  max-width: 52ch;
  margin-inline: auto;
}

/* --- Headline --- */
.contact__headline {
  font-size: var(--text-4xl);
  font-weight: var(--font-extrabold);
  line-height: var(--leading-tight);
  letter-spacing: var(--tracking-tight);
  color: var(--color-text);
}

/* --- Sub-text --- */
.contact__subtext {
  font-size: var(--text-lg);
  line-height: var(--leading-relaxed);
  color: var(--color-text-muted);
}

/* --- Email link --- */
.contact__email {
  display: inline-flex;
  align-items: center;
  gap: var(--space-2);
  font-size: var(--text-base);
  font-weight: var(--font-medium);
  color: var(--color-primary-400);
  text-decoration: none;
  border-bottom: 1px solid rgb(59 130 246 / 0.35);
  padding-bottom: var(--space-0-5);
  transition: color var(--duration-fast) var(--ease-default),
              border-color var(--duration-fast) var(--ease-default);
}

.contact__email:hover {
  color: var(--color-primary-300);
  border-color: var(--color-primary-300);
}

/* --- CTA button (inherits .btn .btn--primary) --- */
.contact__cta {
  font-size: var(--text-lg);
  padding: var(--space-4) var(--space-10);
}

/* =============================================================================
   15. Footer
   ============================================================================= */

.site-footer {
  background: var(--color-neutral-950);
  border-top: 1px solid var(--color-border);
  padding-block: var(--space-10);
}

.footer__container {
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: var(--space-5);
  text-align: center;
}

/* --- Brand row --- */
.footer__brand {
  display: flex;
  align-items: center;
  gap: var(--space-2);
}

.footer__brand-name {
  font-size: var(--text-lg);
  font-weight: var(--font-bold);
  color: var(--color-text);
  letter-spacing: var(--tracking-tight);
}

/* --- Meta: author + affiliation --- */
.footer__meta {
  display: flex;
  flex-direction: column;
  gap: var(--space-1);
}

.footer__author {
  font-size: var(--text-base);
  font-weight: var(--font-semibold);
  color: var(--color-text);
}

.footer__affiliation {
  font-size: var(--text-sm);
  color: var(--color-text-muted);
  line-height: var(--leading-relaxed);
}

/* --- Copyright --- */
.footer__copyright {
  font-size: var(--text-xs);
  color: var(--color-text-subtle);
  letter-spacing: var(--tracking-wide);
}