:root {
    --paper: #F1F3F2;
    --paper-raised: #FAFBFA;
    --ink: #10151B;
    --steel: #5A6470;
    --steel-soft: #88919B;
    --line: #D7DCDD;
    --grid-line: rgba(16, 21, 27, 0.045);
    --signal: #483bf7;
    --signal-ink: #1100ff;
    --signal-soft: rgba(28, 138, 130, 0.09);
    --serif: ui-sans-serif,system-ui,sans-serif,"Apple Color Emoji","Segoe UI Emoji","Segoe UI Symbol","Noto Color Emoji";
    --sans: ui-sans-serif,system-ui,sans-serif,"Apple Color Emoji","Segoe UI Emoji","Segoe UI Symbol","Noto Color Emoji";
    --mono: ui-sans-serif,system-ui,sans-serif,"Apple Color Emoji","Segoe UI Emoji","Segoe UI Symbol","Noto Color Emoji";
  }

  * { box-sizing: border-box; }

  html { -webkit-text-size-adjust: 100%; }

  body {
    margin: 0;
    background: var(--paper);
    color: var(--ink);
    -webkit-font-smoothing: antialiased;
    position: relative;
    font-family: ui-sans-serif, system-ui, sans-serif, "Apple Color Emoji", "Segoe UI Emoji", "Segoe UI Symbol", "Noto Color Emoji";
  }

  body::before {
    content: "";
    position: fixed;
    inset: 0;
    z-index: 0;
    pointer-events: none;
    background-image:
      linear-gradient(var(--grid-line) 1px, transparent 1px),
      linear-gradient(90deg, var(--grid-line) 1px, transparent 1px);
    background-size: 2px 2px;
    mask-image: linear-gradient(to bottom, black, black 60%, transparent 100%);
  }

  main, header.top, footer { position: relative; z-index: 1; }

  a {color: var(--signal-ink);}

  ::selection { background: var(--signal-soft); color: var(--signal-ink); }

  a:focus-visible,
  button:focus-visible {
    outline: 2px solid var(--signal);
    outline-offset: 3px;
  }

  .wrap {
    max-width: 920px;
    margin: 0 auto;
    padding-left: clamp(18px, 5vw, 28px);
     padding-right: clamp(18px, 5vw, 28px);
  }

  /* ---------- header ---------- */

  header.top {padding-top: clamp(20px, 4vw, 32px);padding-left: clamp(18px, 5vw, 28px);padding-right: clamp(18px, 5vw, 28px);}

  .top-row {
    display: flex;
    justify-content: space-between;
    gap: 14px;
    flex-wrap: wrap;
    padding-top: 16px;
    padding-bottom: 16px;
    background: var(--ink);
    border-radius: 8px;
    box-shadow: 1px 5px 10px rgb(0 0 0 / 2%);
    align-items: center;
    color: #fff;
  }

  .mark {
    font-size: 16px;
    letter-spacing: -0.01em;
    color: var(--paper);
    font-weight: 600;
  }

  .mark span { color: var(--steel-soft); }

  .top-right {
    display: flex;
    align-items: baseline;
    gap: 18px;
    font-size: 13px;
  }

  .clock { font-variant-numeric: tabular-nums; white-space: nowrap; }

  .top-cta {
  }

 
  /* ---------- hero ---------- */

  .hero {padding-top: clamp(44px, 8vw, 64px);padding-bottom: clamp(44px, 8vw, 64px);}

  h1 {
    font-weight: 500;
    font-size: clamp(30px, 6.4vw, 46px);
    line-height: 1.14;
    letter-spacing: -0.01em;
    max-width: 19ch;
    margin: 0 0 22px;
  }

  .lede {
    font-size: clamp(16px, 3.6vw, 19px);
    line-height: 1.6;
    color: var(--steel);
    max-width: 56ch;
    margin: 0 0 28px;
  }

  .engines {
    font-size: 13px;
    color: var(--steel-soft);
    display: flex;
    flex-wrap: wrap;
    gap: 8px 18px;
    margin: 0 0 36px;
  }

  .primary-cta {
    display: inline-flex;
    align-items: center;
    gap: 10px;
    font-weight: 500;
    font-size: 16px;
    color: var(--paper-raised);
    background: var(--signal-ink);
    padding: 13px 22px;
    text-decoration: none;
    transition: background 0.15s ease;
    border-radius: 6px;
  }

  .primary-cta:hover, .primary-cta:focus {background: var(--signal);color: var(--paper-raised);}

  /* ---------- diagram ---------- */

  .diagram-section {padding-top: 8px;padding-bottom:  clamp(44px, 8vw, 64px);}

  .diagram {
    background: var(--paper-raised);
    border: 1px solid var(--line);
    padding: clamp(22px, 4vw, 32px) clamp(18px, 4vw, 28px) clamp(18px, 3vw, 24px);
  }

  .diagram-grid {
    display: grid;
    grid-template-columns: 1fr 96px 1fr;
    align-items: center;
    gap: clamp(16px, 3vw, 24px);
  }

  .stage-label {
    display: block;
    
    font-size: 12px;
    color: var(--steel-soft);
    margin-bottom: 8px;
  }

  .stage p {
    margin: 0;
    font-size: clamp(14px, 3.2vw, 15.5px);
    line-height: 1.55;
    color: var(--ink);
  }

  .stage-answer sup {
    
    font-size: 11px;
    color: var(--signal-ink);
    font-weight: 500;
  }

  .track {
    display: flex;
    flex-direction: column;
    align-items: center;
    gap: 8px;
    height: 100%;
  }

  .track-line-wrap {
    position: relative;
    flex: 1;
    width: 100%;
    min-height: 22px;
    display: flex;
    flex-direction: row;
    align-items: center;
    justify-content: space-between;
  }

  .track-line-wrap::before {
    content: "";
    position: absolute;
    top: 50%;
    left: 0;
    right: 0;
    height: 1.4px;
    background: var(--steel-soft);
    transform: scaleX(0);
    transform-origin: left center;
    animation: drawX 1.1s ease-out 0.2s forwards;
  }

  .dot {
    position: relative;
    width: 7px;
    height: 7px;
    border-radius: 50%;
    background: var(--paper-raised);
    border: 1.4px solid var(--steel-soft);
    opacity: 0;
    animation: pop 0.4s ease-out forwards;
  }

  .dot-signal {
    width: 10px;
    height: 10px;
    border-color: var(--signal);
    background: var(--signal-soft);
  }

  .dot:nth-of-type(1) { animation-delay: 0.5s; }
  .dot:nth-of-type(2) { animation-delay: 0.7s; }
  .dot:nth-of-type(3) { animation-delay: 0.9s; }

  .track-caption {
    
    font-size: 11px;
    color: var(--steel-soft);
  }

  @keyframes drawX { to { transform: scaleX(1); } }
  @keyframes drawY { to { transform: scaleY(1); } }
  @keyframes pop { to { opacity: 1; } }

  .citation {
    margin-top: 24px;
    padding-top: 18px;
    border-top: 1px solid var(--line);
    display: flex;
    gap: 10px;
    font-size: 14px;
    line-height: 1.55;
    color: var(--steel);
  }

  .citation-index {
    
    font-size: 12px;
    color: var(--signal-ink);
    flex-shrink: 0;
  }

  @media (prefers-reduced-motion: reduce) {
    .track-line-wrap::before { animation: none; transform: scaleX(1); }
    .dot { animation: none; opacity: 1; }
    .pulse { animation: none !important; }
  }

  /* ---------- what's changed ---------- */

  .changed {border-top: 1px solid var(--line);padding-top: 8px;padding-bottom: clamp(44px, 8vw, 64px);}

  .section-heading {
    
    font-weight: 500;
    font-size: clamp(20px, 4vw, 24px);
    margin: clamp(36px, 6vw, 48px) 0 clamp(20px, 4vw, 28px);
  }

  .changed-grid {
    display: grid;
    grid-template-columns: repeat(3, 1fr);
    gap: clamp(20px, 4vw, 28px);
  }

  .changed-grid p {
    margin: 0;
    font-size: 15px;
    line-height: 1.65;
    color: var(--steel);
  }

  .changed-grid strong {
    display: block;
   
    font-weight: 500;
    color: var(--ink);
    font-size: 15.5px;
    margin-bottom: 8px;
  }

  /* ---------- process ---------- */

  .process {border-top: 1px solid var(--line);padding-top: 8px;padding-bottom: clamp(48px, 8vw, 72px);}

  .process-list { margin: 0; padding: 0; list-style: none; }

  .process-item {
    display: grid;
    grid-template-columns: 40px 1fr;
    gap: clamp(14px, 3vw, 20px);
    padding: clamp(16px, 3vw, 22px) 0;
    border-top: 1px solid var(--line);
  }

  .process-item:last-child { border-bottom: 1px solid var(--line); }

  .process-index {
    
    font-size: 13px;
    color: var(--signal-ink);
    padding-top: 2px;
  }

  .process-item h3 {
   
    font-weight: 500;
    font-size: 16.5px;
    margin: 0 0 6px;
    display: flex;
    align-items: center;
    gap: 8px;
  }

  .pulse-dot {
    width: 6px;
    height: 6px;
    border-radius: 50%;
    background: var(--signal);
    flex-shrink: 0;
  }

  .pulse { animation: livepulse 2.4s ease-in-out infinite; }

  @keyframes livepulse {
    0%, 100% { opacity: 1; box-shadow: 0 0 0 0 rgba(28,138,130,0.35); }
    50% { opacity: 0.55; box-shadow: 0 0 0 4px rgba(28,138,130,0); }
  }

  .process-item p {
    margin: 0;
    font-size: 15px;
    line-height: 1.6;
    color: var(--steel);
    max-width: 56ch;
  }

  /* ---------- close / footer ---------- */

  .close {padding-top: 8px;padding-bottom: clamp(36px, 6vw, 56px);}

  .close-inner { padding: clamp(36px, 6vw, 48px) 0 0; }

  .close h2 {
    font-weight: 500;
    font-size: clamp(22px, 4.4vw, 28px);
    margin: 0 0 16px;
    max-width: 24ch;
  }

  .close p {
    font-size: 16px;
    color: var(--steel);
    margin: 0 0 24px;
  }

  footer {
    padding: 28px 0 clamp(40px, 8vw, 60px);
    display: flex;
    justify-content: space-between;
    align-items: center;
    gap: 12px 16px;
    
    font-size: 12.5px;
    color: var(--steel-soft);
    flex-wrap: wrap;
  }

  footer a {
    color: var(--steel);
    text-decoration: none;
    border-bottom: 1px solid var(--line);
  }

  footer a:hover { color: var(--signal-ink); border-color: var(--signal); }

  /* ---------- responsive: diagram stacks, track rotates to vertical ---------- */

  @media (max-width: 680px) {
    .diagram-grid { grid-template-columns: 1fr; }

    .track {
      flex-direction: row;
      width: 100%;
      height: auto;
      padding: 4px 0;
    }

    .track-line-wrap {
      flex-direction: row;
      min-height: 0;
      height: 22px;
    }

    .track-caption { writing-mode: horizontal-tb; }
  }

  @media (max-width: 560px) {
    .changed-grid { grid-template-columns: 1fr; }
    .process-item { grid-template-columns: 28px 1fr; }
    .top-right {gap: 12px;display: none;}
  }

  @media (max-width: 420px) {
    h1 { max-width: 100%; }
    .primary-cta { width: 100%; justify-content: center; }
    .clock { display: none; }
  }