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

  :root {
    --bg:        #152639;
    --panel:     #1c3249;
    --border:    #243d55;
    --cyan:      #0aadce;
    --cyan-dim:  rgba(10,173,206,.12);
    --cyan-glow: rgba(10,173,206,.35);
    --text:      #e8f2fa;
    --muted:     #6d90aa;
  }

  html, body {
    height: 100%;
    font-family: 'Barlow', sans-serif;
  }

  body {
    display: grid;
    place-items: center;
    min-height: 100vh;
    background: var(--bg);
    background-image: radial-gradient(ellipse 80% 60% at 50% 45%, #1d3d5a 0%, #152639 70%);
    overflow: hidden;
  }

  /* ── rings ── */
  .rings {
    position: fixed;
    inset: 0;
    pointer-events: none;
  }
  .rings span {
    position: absolute;
    border-radius: 50%;
    border: 1px solid rgba(10,173,206,.06);
    top: 50%; left: 50%;
    transform: translate(-50%, -50%);
    animation: pulse 6s ease-in-out infinite;
  }
  .rings span:nth-child(1) { width: 480px;  height: 480px;  animation-delay: 0s; }
  .rings span:nth-child(2) { width: 720px;  height: 720px;  animation-delay: 1s; }
  .rings span:nth-child(3) { width: 960px;  height: 960px;  animation-delay: 2s; }
  .rings span:nth-child(4) { width: 1200px; height: 1200px; animation-delay: 3s; }

  @keyframes pulse {
    0%, 100% { opacity: .4; }
    50%       { opacity: 1;  }
  }

  /* ── content ── */
  .container {
    position: relative;
    text-align: center;
    padding: 0 24px;
    animation: fadeUp .6s ease both;
  }

  @keyframes fadeUp {
    from { opacity: 0; transform: translateY(24px); }
    to   { opacity: 1; transform: translateY(0); }
  }

  /* ── big 404 ── */
  .number {
    font-family: 'Barlow Condensed', sans-serif;
    font-size: clamp(120px, 20vw, 200px);
    font-weight: 700;
    line-height: 1;
    letter-spacing: -4px;
    /* cyan glow effect */
    color: transparent;
    -webkit-text-stroke: 2px var(--cyan);
    text-shadow:
      0 0 40px var(--cyan-glow),
      0 0 80px rgba(10,173,206,.15);
    user-select: none;
  }

  /* signal icon between 4 and 4 */
  .signal {
    display: inline-block;
    width: clamp(60px, 10vw, 100px);
    height: clamp(60px, 10vw, 100px);
    vertical-align: middle;
    margin: 0 -8px 16px;
  }

  /* ── logo ── */
  .logo {
    display: flex;
    align-items: center;
    justify-content: center;
    gap: 6px;
    margin-bottom: 20px;
  }
  .logo-text {
    font-size: 18px;
    font-weight: 700;
    letter-spacing: .5px;
  }
  .logo-text .white { color: #fff; }
  .logo-text .cyan  { color: var(--cyan); }
  .logo-icon {
    width: 20px; height: 20px; flex-shrink: 0;
  }

  /* ── divider ── */
  .divider {
    width: 60px;
    height: 2px;
    background: linear-gradient(90deg, transparent, var(--cyan), transparent);
    margin: 0 auto 24px;
    border-radius: 2px;
  }

  /* ── text ── */
  h1 {
    font-size: clamp(18px, 3vw, 24px);
    font-weight: 600;
    color: var(--text);
    margin-bottom: 10px;
  }

  p {
    font-size: 15px;
    color: var(--muted);
    max-width: 380px;
    margin: 0 auto 32px;
    line-height: 1.6;
    font-weight: 400;
  }

  /* ── button ── */
  .btn {
    display: inline-flex;
    align-items: center;
    gap: 8px;
    padding: 12px 28px;
    background: var(--cyan);
    border: none;
    border-radius: 8px;
    color: #0d2030;
    font-family: 'Barlow', sans-serif;
    font-size: 16px;
    font-weight: 700;
    letter-spacing: .5px;
    cursor: pointer;
    text-decoration: none;
    transition: filter .2s, box-shadow .2s, transform .1s;
  }
  .btn:hover {
    filter: brightness(1.1);
    box-shadow: 0 6px 28px var(--cyan-glow);
  }
  .btn:active { transform: scale(.97); }
  .btn svg { width: 16px; height: 16px; }

  /* ── footer ── */
  .footer {
    position: fixed;
    bottom: 20px;
    left: 0; right: 0;
    text-align: center;
    font-size: 11px;
    color: rgba(109,144,170,.4);
    letter-spacing: .5px;
  }