:root {
  color-scheme: light dark;
  --bg: #f7f8fc;
  --surface: rgba(255, 255, 255, 0.86);
  --surface-solid: #ffffff;
  --ink: #172033;
  --muted: #5f6b7d;
  --line: #dbe1ea;
  --accent: #1268d6;
  --accent-strong: #0756b7;
  --accent-soft: #e8f1ff;
  --success: #117d55;
  --shadow: 0 24px 64px rgba(40, 57, 86, 0.12);
  --radius: 24px;
  font-family: -apple-system, BlinkMacSystemFont, "SF Pro Display", "Segoe UI", sans-serif;
}

* { box-sizing: border-box; }

html { scroll-behavior: smooth; }

body {
  margin: 0;
  min-height: 100vh;
  background:
    radial-gradient(circle at 10% 0%, rgba(72, 150, 255, 0.18), transparent 36rem),
    radial-gradient(circle at 96% 16%, rgba(106, 214, 175, 0.16), transparent 32rem),
    var(--bg);
  color: var(--ink);
  line-height: 1.6;
}

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

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

a:focus-visible,
button:focus-visible {
  outline: 3px solid rgba(18, 104, 214, 0.35);
  outline-offset: 4px;
}

.shell {
  width: min(1120px, calc(100% - 40px));
  margin: 0 auto;
}

.site-header {
  position: sticky;
  top: 0;
  z-index: 10;
  border-bottom: 1px solid rgba(219, 225, 234, 0.74);
  background: rgba(247, 248, 252, 0.82);
  -webkit-backdrop-filter: blur(18px);
  backdrop-filter: blur(18px);
}

.nav {
  min-height: 68px;
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 24px;
}

.brand {
  display: inline-flex;
  align-items: center;
  gap: 11px;
  color: var(--ink);
  font-weight: 760;
  text-decoration: none;
  letter-spacing: -0.02em;
}

.brand-mark {
  width: 36px;
  height: 36px;
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  gap: 2px;
  padding: 6px;
  border-radius: 10px;
  background: var(--ink);
  box-shadow: 0 8px 20px rgba(23, 32, 51, 0.2);
}

.brand-mark span { border-radius: 2px; background: #fff; }
.brand-mark span:nth-child(2),
.brand-mark span:nth-child(6),
.brand-mark span:nth-child(7) { background: #71b4ff; }

.nav-links { display: flex; gap: 22px; }
.nav-links a { color: var(--muted); font-weight: 620; text-decoration: none; }
.nav-links a:hover { color: var(--ink); }

.hero {
  min-height: 680px;
  display: grid;
  grid-template-columns: minmax(0, 1.12fr) minmax(340px, 0.88fr);
  align-items: center;
  gap: 76px;
  padding: 88px 0 76px;
}

.eyebrow {
  display: inline-flex;
  align-items: center;
  gap: 8px;
  margin: 0 0 18px;
  color: var(--success);
  font-size: 0.88rem;
  font-weight: 780;
  letter-spacing: 0.08em;
  text-transform: uppercase;
}

.eyebrow::before {
  content: "";
  width: 9px;
  height: 9px;
  border-radius: 50%;
  background: currentColor;
  box-shadow: 0 0 0 6px rgba(17, 125, 85, 0.12);
}

h1, h2, h3 { line-height: 1.12; letter-spacing: -0.035em; }

h1 {
  max-width: 760px;
  margin: 0;
  font-size: clamp(3rem, 7vw, 5.8rem);
  font-weight: 820;
}

.hero-copy {
  max-width: 690px;
  margin: 26px 0 0;
  color: var(--muted);
  font-size: clamp(1.12rem, 2vw, 1.35rem);
}

.actions { display: flex; flex-wrap: wrap; gap: 14px; margin-top: 34px; }

.button {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  min-height: 52px;
  padding: 0 22px;
  border-radius: 15px;
  font-weight: 750;
  text-decoration: none;
  transition: transform 160ms ease, box-shadow 160ms ease, background 160ms ease;
}

.button:hover { transform: translateY(-2px); }
.button-primary { color: #fff; background: var(--accent); box-shadow: 0 14px 30px rgba(18, 104, 214, 0.24); }
.button-primary:hover { color: #fff; background: var(--accent-strong); }
.button-secondary { color: var(--ink); border: 1px solid var(--line); background: var(--surface); }
.button-secondary:hover { color: var(--ink); box-shadow: 0 12px 26px rgba(40, 57, 86, 0.1); }

.trust-row {
  display: flex;
  flex-wrap: wrap;
  gap: 12px 22px;
  margin: 28px 0 0;
  padding: 0;
  color: var(--muted);
  list-style: none;
  font-size: 0.95rem;
  font-weight: 650;
}

.trust-row li::before { content: "✓"; margin-right: 7px; color: var(--success); font-weight: 900; }

.board-card {
  position: relative;
  border: 1px solid rgba(219, 225, 234, 0.9);
  border-radius: 32px;
  padding: 30px;
  background: var(--surface);
  box-shadow: var(--shadow);
}

.board-card::before {
  content: "NO ADS · OFFLINE";
  position: absolute;
  top: -15px;
  right: 24px;
  padding: 7px 13px;
  border-radius: 999px;
  color: #fff;
  background: var(--success);
  font-size: 0.72rem;
  font-weight: 820;
  letter-spacing: 0.07em;
}

.sudoku-board {
  display: grid;
  grid-template-columns: repeat(9, 1fr);
  aspect-ratio: 1;
  overflow: hidden;
  border: 3px solid var(--ink);
  border-radius: 10px;
  background: var(--surface-solid);
}

.cell {
  display: grid;
  place-items: center;
  border-right: 1px solid var(--line);
  border-bottom: 1px solid var(--line);
  color: var(--ink);
  font-size: clamp(1rem, 2.4vw, 1.55rem);
  font-weight: 690;
}

.cell:nth-child(3n) { border-right: 2px solid var(--ink); }
.cell:nth-child(9n) { border-right: 0; }
.cell:nth-child(n+19):nth-child(-n+27),
.cell:nth-child(n+46):nth-child(-n+54) { border-bottom: 2px solid var(--ink); }
.cell:nth-child(n+73) { border-bottom: 0; }
.cell.accent { color: var(--accent); background: var(--accent-soft); }

.board-meta {
  display: flex;
  justify-content: space-between;
  gap: 16px;
  margin-top: 22px;
  color: var(--muted);
  font-weight: 650;
}

.section { padding: 84px 0; }
.section-heading { max-width: 720px; margin-bottom: 38px; }
.section-heading h2 { margin: 0 0 16px; font-size: clamp(2.1rem, 5vw, 3.4rem); }
.section-heading p { margin: 0; color: var(--muted); font-size: 1.15rem; }

.feature-grid { display: grid; grid-template-columns: repeat(3, 1fr); gap: 18px; }

.feature-card {
  min-height: 230px;
  padding: 28px;
  border: 1px solid var(--line);
  border-radius: var(--radius);
  background: var(--surface);
}

.feature-icon {
  width: 44px;
  height: 44px;
  display: grid;
  place-items: center;
  margin-bottom: 26px;
  border-radius: 13px;
  color: var(--accent);
  background: var(--accent-soft);
  font-size: 1.25rem;
  font-weight: 820;
}

.feature-card h3 { margin: 0 0 10px; font-size: 1.3rem; }
.feature-card p { margin: 0; color: var(--muted); }

.promise {
  display: grid;
  grid-template-columns: 1fr auto;
  align-items: center;
  gap: 48px;
  padding: 48px;
  border-radius: 30px;
  color: #fff;
  background: linear-gradient(135deg, #172033, #1e477b);
  box-shadow: var(--shadow);
}

.promise h2 { margin: 0 0 12px; font-size: clamp(2rem, 5vw, 3.2rem); }
.promise p { max-width: 680px; margin: 0; color: rgba(255, 255, 255, 0.76); font-size: 1.08rem; }
.promise .button { color: var(--ink); background: #fff; white-space: nowrap; }

.page-hero { max-width: 800px; padding: 92px 0 48px; }
.page-hero h1 { font-size: clamp(2.8rem, 7vw, 4.7rem); }
.page-hero p { max-width: 700px; color: var(--muted); font-size: 1.2rem; }

.content-card {
  max-width: 880px;
  margin-bottom: 80px;
  padding: clamp(28px, 5vw, 54px);
  border: 1px solid var(--line);
  border-radius: 28px;
  background: var(--surface);
  box-shadow: 0 20px 50px rgba(40, 57, 86, 0.08);
}

.content-card h2 { margin: 42px 0 12px; font-size: 1.65rem; }
.content-card h2:first-child { margin-top: 0; }
.content-card h3 { margin: 28px 0 8px; font-size: 1.18rem; }
.content-card p, .content-card li { color: var(--muted); }
.content-card ul { padding-left: 1.3rem; }
.content-card .contact-box { padding: 22px; border-radius: 18px; background: var(--accent-soft); }
.content-card .contact-box p { margin: 0; color: var(--ink); }

.site-footer {
  padding: 36px 0 44px;
  border-top: 1px solid var(--line);
  color: var(--muted);
  font-size: 0.92rem;
}

.footer-row { display: flex; justify-content: space-between; gap: 22px; flex-wrap: wrap; }
.footer-links { display: flex; gap: 18px; }
.footer-links a { color: var(--muted); text-decoration: none; }

@media (max-width: 860px) {
  .hero { grid-template-columns: 1fr; gap: 64px; padding-top: 70px; }
  .board-card { width: min(560px, 100%); margin: 0 auto; }
  .feature-grid { grid-template-columns: 1fr 1fr; }
  .promise { grid-template-columns: 1fr; }
}

@media (max-width: 600px) {
  .shell { width: min(100% - 28px, 1120px); }
  .site-header { position: static; }
  .nav { align-items: flex-start; padding: 15px 0; }
  .nav-links { gap: 14px; font-size: 0.9rem; }
  .hero { min-height: 0; padding: 62px 0; }
  .feature-grid { grid-template-columns: 1fr; }
  .promise { padding: 32px 26px; }
  .board-card { padding: 20px; }
  .board-meta { font-size: 0.86rem; }
}

@media (prefers-reduced-motion: reduce) {
  html { scroll-behavior: auto; }
  .button { transition: none; }
}

@media (prefers-color-scheme: dark) {
  :root {
    --bg: #0d121c;
    --surface: rgba(24, 32, 46, 0.9);
    --surface-solid: #151d2a;
    --ink: #f2f5fa;
    --muted: #abb5c4;
    --line: #334055;
    --accent: #70adff;
    --accent-strong: #9bc5ff;
    --accent-soft: #1d385c;
    --success: #67d6aa;
  }
  .site-header { background: rgba(13, 18, 28, 0.84); border-color: rgba(51, 64, 85, 0.75); }
  .brand-mark { background: #f2f5fa; }
  .brand-mark span { background: #182032; }
  .button-primary { color: #071528; background: #70adff; }
  .button-primary:hover { color: #071528; background: #9bc5ff; }
  .promise { background: linear-gradient(135deg, #1b2b43, #173e70); }
  .promise .button { color: #172033; }
}