:root {
    --font-display: "Space Grotesk", system-ui, sans-serif;
    --font-sans: "Inter", system-ui, sans-serif;
    --font-mono: "JetBrains Mono", ui-monospace, monospace;

    --text-sm: 14px; --text-base: 16px; --text-lg: 18px;
    --text-xl: 20px; --text-2xl: 24px; --text-4xl: 36px; --text-5xl: 48px;

    --space-1: 4px; --space-2: 8px; --space-3: 12px; --space-4: 16px;
    --space-5: 20px; --space-6: 24px; --space-8: 32px; --space-10: 40px;
    --space-12: 48px; --space-16: 64px; --space-20: 80px;

    --radius-md: 10px; --radius-lg: 14px; --radius-xl: 20px; --radius-full: 999px;

    --shadow-sm: 0 1px 2px rgba(18, 21, 33, 0.06), 0 1px 3px rgba(18, 21, 33, 0.08);
    --shadow-md: 0 4px 12px rgba(18, 21, 33, 0.1);
    --shadow-glow: 0 0 0 1px rgba(91, 70, 232, 0.25), 0 8px 24px rgba(91, 70, 232, 0.35);

    --motion-fast: 120ms; --motion: 200ms;
    --ease: cubic-bezier(0.16, 1, 0.3, 1);

    --spectral: linear-gradient(100deg, #a855f7 0%, #6366f1 34%, #3b82f6 66%, #22d3ee 100%);

    /* light roles */
    --color-bg-base: #f6f7f9;
    --color-bg-subtle: #eceef3;
    --color-surface: #ffffff;
    --color-text: #121521;
    --color-text-secondary: #495168;
    --color-text-tertiary: #697089;
    --color-text-on-accent: #ffffff;
    --color-border: #dde1ea;
    --color-border-strong: #c3c9d8;
    --color-border-focus: #5b46e8;
    --color-accent: #5b46e8;
    --color-accent-hover: #4a37c9;
    --color-accent-active: #3c2da3;
    --color-accent-subtle: #efedfe;
    --color-accent-text: #4a37c9;
  }

  [data-theme="dark"] {
    --shadow-sm: 0 1px 2px rgba(0, 0, 0, 0.4), 0 1px 3px rgba(0, 0, 0, 0.5);
    --shadow-md: 0 4px 12px rgba(0, 0, 0, 0.5);
    --shadow-glow: 0 0 0 1px rgba(110, 91, 242, 0.35), 0 8px 24px rgba(110, 91, 242, 0.45);

    --color-bg-base: #0a0b12;
    --color-bg-subtle: #11131c;
    --color-surface: #141824;
    --color-text: #f3f5f9;
    --color-text-secondary: #aeb6c8;
    --color-text-tertiary: #788299;
    --color-text-on-accent: #ffffff;
    --color-border: #272c3b;
    --color-border-strong: #394056;
    --color-border-focus: #8a76f4;
    --color-accent: #6e5bf2;
    --color-accent-hover: #8a76f4;
    --color-accent-active: #a899f8;
    --color-accent-subtle: rgba(110, 91, 242, 0.16);
    --color-accent-text: #a899f8;
  }

  * { box-sizing: border-box; }
  html { -webkit-text-size-adjust: 100%; }
  body {
    margin: 0;
    font-family: var(--font-sans);
    font-size: var(--text-base);
    line-height: 24px;
    color: var(--color-text);
    background: var(--color-bg-base);
  }

  a { color: var(--color-accent-text); text-decoration: none; }
  a:hover { text-decoration: underline; text-underline-offset: 3px; }

  :focus-visible {
    outline: 2px solid var(--color-border-focus);
    outline-offset: 2px;
    border-radius: var(--radius-md);
  }

  .container { max-width: 1080px; margin: 0 auto; padding: 0 var(--space-4); }
  @media (min-width: 768px) { .container { padding: 0 var(--space-6); } }
  @media (min-width: 1024px) { .container { padding: 0 var(--space-8); } }

  /* App shell top bar */
  header.shell {
    position: sticky; top: 0; z-index: 10;
    background: color-mix(in srgb, var(--color-bg-base) 80%, transparent);
    backdrop-filter: blur(8px);
    border-bottom: 1px solid var(--color-border);
  }
  .shell .bar {
    display: flex; align-items: center; justify-content: space-between;
    height: 64px;
  }
  .brand {
    display: inline-flex; align-items: center; gap: var(--space-2);
    color: var(--color-text); text-decoration: none;
    border-radius: var(--radius-md);
    transition: opacity var(--motion-fast) var(--ease);
  }
  .brand:hover { text-decoration: none; opacity: 0.72; }
  .mark {
    width: 28px; height: 28px; border-radius: 8px;
    background: var(--spectral);
  }
  .wordmark {
    font-family: var(--font-display); font-weight: 700; font-size: var(--text-xl);
    letter-spacing: -0.02em;
  }

  /* Buttons */
  .btn {
    display: inline-flex; align-items: center; justify-content: center; gap: var(--space-2);
    height: 40px; padding: 0 var(--space-4);
    font-family: var(--font-sans); font-size: var(--text-sm); font-weight: 600;
    border-radius: var(--radius-md); border: 1px solid transparent;
    white-space: nowrap; cursor: pointer;
    transition: background var(--motion-fast) var(--ease), transform var(--motion-fast) var(--ease);
  }
  .btn:active { transform: translateY(1px); }
  .btn-lg { height: 48px; padding: 0 var(--space-5); font-size: var(--text-base); }
  .btn-primary { background: var(--color-accent); color: var(--color-text-on-accent); box-shadow: var(--shadow-glow); }
  .btn-primary:hover { background: var(--color-accent-hover); }
  .btn-primary:active { background: var(--color-accent-active); }
  .btn-secondary { background: var(--color-surface); color: var(--color-text); border-color: var(--color-border-strong); }
  .btn-secondary:hover { background: var(--color-bg-subtle); }
  .btn-ghost { background: transparent; color: var(--color-text); }
  .btn-ghost:hover { background: var(--color-bg-subtle); }
  .btn-icon { width: 40px; height: 40px; padding: 0; }
  .btn:disabled { opacity: 0.47; cursor: not-allowed; }

  /* Hero */
  .hero {
    position: relative; overflow: hidden; text-align: center;
    padding: var(--space-16) 0 var(--space-16);
  }
  @media (min-width: 768px) { .hero { padding: var(--space-20) 0 var(--space-20); } }
  /* One calm ambient glow — the single hero highlight the system allows. */
  .aura {
    position: absolute; left: 50%; top: 0; transform: translateX(-50%);
    width: 760px; max-width: 120%; height: 480px;
    background: var(--spectral); filter: blur(140px); opacity: 0.22;
    border-radius: var(--radius-full); pointer-events: none; z-index: 0;
  }
  [data-theme="dark"] .aura { opacity: 0.36; }
  .hero > *:not(.aura) { position: relative; z-index: 1; }
  .eyebrow {
    display: inline-block; font-size: var(--text-sm); font-weight: 600;
    letter-spacing: 0.04em; text-transform: uppercase; color: var(--color-accent-text);
    padding: var(--space-1) var(--space-3); border-radius: var(--radius-full);
    background: var(--color-accent-subtle); margin-bottom: var(--space-5);
  }
  h1 {
    font-family: var(--font-display); font-weight: 700;
    font-size: var(--text-4xl); line-height: 1.05; letter-spacing: -0.035em;
    margin: 0 0 var(--space-5);
  }
  h1 .spectral {
    background: var(--spectral);
    -webkit-background-clip: text; background-clip: text; color: transparent;
  }
  .lead {
    font-size: var(--text-lg); line-height: 28px; color: var(--color-text-secondary);
    max-width: 600px; margin: 0 auto var(--space-8);
  }
  .cta-row { display: flex; gap: var(--space-3); justify-content: center; flex-wrap: wrap; }
  @media (min-width: 768px) { h1 { font-size: var(--text-5xl); } }

  /* Principles */
  .features { padding: var(--space-8) 0 var(--space-20); }
  .grid { display: grid; gap: var(--space-4); grid-template-columns: 1fr; }
  @media (min-width: 768px) { .grid { grid-template-columns: repeat(3, 1fr); gap: var(--space-6); } }
  /* Flat and calm: one hairline border, no shadow, a quiet lift on hover. */
  .card {
    background: var(--color-surface); border-radius: var(--radius-lg);
    padding: var(--space-8); border: 1px solid var(--color-border);
    transition: border-color var(--motion) var(--ease), transform var(--motion) var(--ease);
  }
  .card:hover { border-color: var(--color-border-strong); transform: translateY(-2px); }
  .card .ico {
    width: 40px; height: 40px; display: grid; place-items: center;
    border-radius: var(--radius-md); background: var(--color-accent-subtle);
    color: var(--color-accent-text); margin-bottom: var(--space-5);
  }
  .card h3 {
    font-family: var(--font-display); font-weight: 600; font-size: var(--text-xl);
    letter-spacing: -0.02em; margin: 0 0 var(--space-2);
  }
  .card p { margin: 0; color: var(--color-text-secondary); font-size: var(--text-sm); line-height: 20px; }

  footer.site {
    border-top: 1px solid var(--color-border);
    padding: var(--space-8) 0;
    color: var(--color-text-tertiary); font-size: var(--text-sm);
  }
  footer .bar { display: flex; align-items: center; justify-content: center; gap: var(--space-2); }

  @media (prefers-reduced-motion: reduce) {
    * { transition: none !important; animation: none !important; }
  }