:root {
  --color-primary: #1a3a6b;
  --color-primary-dark: #0d2240;
  --color-primary-light: #2a5298;
  --color-accent: #c0392b;
  --color-accent-dark: #962d22;
  --color-white: #ffffff;
  --color-bg: #f5f7fa;
  --color-text: #2c3e50;
  --color-text-light: #6b7c93;
  --color-border: #e1e8ef;

  --font-stack: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Oxygen,
    Ubuntu, Cantarell, "Helvetica Neue", Arial, sans-serif;

  --spacing-xs: 0.5rem;
  --spacing-sm: 1rem;
  --spacing-md: 1.5rem;
  --spacing-lg: 2rem;
  --spacing-xl: 3rem;
  --spacing-2xl: 4rem;
  --spacing-3xl: 6rem;

  --max-width: 1200px;
  --nav-height: 72px;
  --radius-sm: 4px;
  --radius: 8px;
  --radius-lg: 16px;
  --shadow-sm: 0 1px 3px rgba(0, 0, 0, 0.08);
  --shadow: 0 4px 20px rgba(0, 0, 0, 0.08);
  --shadow-lg: 0 8px 40px rgba(0, 0, 0, 0.12);
  --transition: 0.3s ease;
  --transition-fast: 0.15s ease;
}

/* ── Reset ── */

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

html {
  scroll-behavior: smooth;
  scroll-padding-top: var(--nav-height);
}

body {
  font-family: var(--font-stack);
  font-size: 1rem;
  line-height: 1.6;
  color: var(--color-text);
  background: var(--color-white);
  -webkit-font-smoothing: antialiased;
  -moz-osx-font-smoothing: grayscale;
}

/* ── Typography ── */

h1, h2, h3, h4, h5, h6 {
  color: var(--color-primary);
  line-height: 1.2;
  font-weight: 700;
}

h1 { font-size: clamp(2rem, 5vw, 3.5rem); }
h2 { font-size: clamp(1.5rem, 3.5vw, 2.5rem); }
h3 { font-size: clamp(1.25rem, 2.5vw, 1.75rem); }
h4 { font-size: 1.25rem; }

p { margin-bottom: var(--spacing-sm); }
p:last-child { margin-bottom: 0; }

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

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

img {
  max-width: 100%;
  display: block;
}

ul, ol { list-style: none; }

.ai { color: var(--color-accent); }

/* ── Layout ── */

.container {
  max-width: var(--max-width);
  margin: 0 auto;
  padding: 0 var(--spacing-lg);
}

.section {
  padding: var(--spacing-3xl) 0;
}

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

.section-header {
  text-align: center;
  margin-bottom: var(--spacing-2xl);
}

.section-header h2 {
  margin-bottom: var(--spacing-sm);
}

.section-header p {
  color: var(--color-text-light);
  max-width: 640px;
  margin: 0 auto;
  font-size: 1.125rem;
}

/* ── Grid ── */

.grid {
  display: grid;
  gap: var(--spacing-lg);
}

.grid--2 { grid-template-columns: repeat(2, 1fr); }
.grid--3 { grid-template-columns: repeat(3, 1fr); }
.grid--4 { grid-template-columns: repeat(4, 1fr); }

/* ── Animations ── */

.fade-in {
  opacity: 0;
  transform: translateY(30px);
  transition: opacity 0.6s ease, transform 0.6s ease;
}

.fade-in.visible {
  opacity: 1;
  transform: translateY(0);
}

.fade-in-left {
  opacity: 0;
  transform: translateX(-30px);
  transition: opacity 0.6s ease, transform 0.6s ease;
}

.fade-in-left.visible {
  opacity: 1;
  transform: translateX(0);
}

.fade-in-right {
  opacity: 0;
  transform: translateX(30px);
  transition: opacity 0.6s ease, transform 0.6s ease;
}

.fade-in-right.visible {
  opacity: 1;
  transform: translateX(0);
}

/* stagger children inside grids */
.grid .fade-in:nth-child(2) { transition-delay: 0.1s; }
.grid .fade-in:nth-child(3) { transition-delay: 0.2s; }
.grid .fade-in:nth-child(4) { transition-delay: 0.3s; }
.grid .fade-in:nth-child(5) { transition-delay: 0.4s; }

/* ── Responsive ── */

@media (max-width: 1024px) {
  .grid--4 { grid-template-columns: repeat(2, 1fr); }
  .grid--3 { grid-template-columns: repeat(2, 1fr); }
}

@media (max-width: 768px) {
  .grid--4,
  .grid--3,
  .grid--2 { grid-template-columns: 1fr; }

  .container { padding: 0 var(--spacing-sm); }
  .section { padding: var(--spacing-2xl) 0; }
}