:root {
    /* engineering paper: cool grey-green, not cream */
    --paper:      #EFF2F1;
    --paper-2:    #E5EAE8;
    --card:       #F7F9F8;
    --ink:        #12181A;
    --ink-2:      #3D4A4D;
    --ink-3:      #6D7B7E;
    --rule:       #CBD4D2;
    --rule-2:     #DCE3E1;
    --water:      #06696B;
    --water-soft: #D3E5E4;
    --ochre:      #96560F;
    --ochre-soft: #F2E4D2;
    --term-bg:    #101617;
    --term-ink:   #CFDAD9;

    --step: clamp(0.9rem, 0.6rem + 0.9vw, 1.35rem);
    color-scheme: light;
  }

  @media (prefers-color-scheme: dark) {
    :root:not([data-theme="light"]) {
      --paper:      #0C1112;
      --paper-2:    #0F1516;
      --card:       #141B1C;
      --ink:        #E2EAE9;
      --ink-2:      #A9B8B7;
      --ink-3:      #768786;
      --rule:       #253032;
      --rule-2:     #1B2324;
      --water:      #5FCFCB;
      --water-soft: #14312F;
      --ochre:      #D6A05C;
      --ochre-soft: #2C2418;
      --term-bg:    #070B0C;
      --term-ink:   #CFDAD9;
      color-scheme: dark;
    }
  }

  * { box-sizing: border-box; }

  body {
    margin: 0;
    background: var(--paper);
    color: var(--ink);
    font-family: "Newsreader", Georgia, "Times New Roman", serif;
    font-size: 1.0625rem;
    line-height: 1.6;
    -webkit-font-smoothing: antialiased;
  }

  .mono, code, kbd {
    font-family: "JetBrains Mono", ui-monospace, SFMono-Regular, Menlo, Consolas, monospace;
  }

  h1, h2, h3 {
    font-family: "Bricolage Grotesque", "Helvetica Neue", Arial, sans-serif;
    font-weight: 700;
    text-wrap: balance;
    margin: 0;
    letter-spacing: -0.015em;
  }

  .label {
    font-family: "JetBrains Mono", monospace;
    font-size: 0.7rem;
    font-weight: 500;
    letter-spacing: 0.13em;
    text-transform: uppercase;
    color: var(--ink-3);
  }

  /* ---------------- masthead ---------------- */

  header.top {
    border-bottom: 1px solid var(--rule);
    background: var(--paper-2);
  }

  .top-inner {
    max-width: 1180px;
    margin: 0 auto;
    padding: clamp(1.6rem, 4vw, 3rem) clamp(1.1rem, 3vw, 2.2rem) clamp(1.4rem, 3vw, 2.2rem);
    display: grid;
    gap: 1.5rem;
  }

  .eyebrow {
    display: flex;
    flex-wrap: wrap;
    gap: 0.5rem 1.1rem;
    align-items: baseline;
  }

  h1 {
    font-size: clamp(2rem, 1.1rem + 3.6vw, 3.4rem);
    line-height: 1.02;
    max-width: 16ch;
  }

  .standfirst {
    max-width: 56ch;
    color: var(--ink-2);
    font-size: 1.1rem;
  }

  .facts {
    display: flex;
    flex-wrap: wrap;
    gap: 0 2rem;
    border-top: 1px solid var(--rule);
    padding-top: 0.9rem;
  }

  .fact { display: grid; gap: 0.15rem; padding: 0.3rem 0; }
  .fact b {
    font-family: "JetBrains Mono", monospace;
    font-size: 0.9rem;
    font-weight: 500;
    color: var(--ink);
    font-variant-numeric: tabular-nums;
  }

  /* ---------------- the transformation strip ---------------- */

  figure.strip {
    margin: 0;
    border: 1px solid var(--rule);
    background: var(--card);
    padding: clamp(1rem, 2.5vw, 1.6rem);
    overflow-x: auto;
  }

  .strip-row { display: flex; align-items: center; gap: 0.28rem; min-width: max-content; }
  .strip-row + .strip-row { margin-top: 0.9rem; }

  .ch {
    font-family: "JetBrains Mono", monospace;
    font-size: 0.95rem;
    width: 1.7rem;
    height: 2rem;
    display: grid;
    place-items: center;
    border: 1px solid var(--rule);
    color: var(--ink-2);
    background: var(--paper);
  }
  .ch.sp { color: var(--ink-3); background: var(--paper-2); }

  .arrows {
    display: flex;
    gap: 0.28rem;
    color: var(--ink-3);
    font-family: "JetBrains Mono", monospace;
    font-size: 0.75rem;
    min-width: max-content;
    margin: 0.45rem 0;
  }

  .tok {
    font-family: "JetBrains Mono", monospace;
    font-size: 0.78rem;
    letter-spacing: 0.04em;
    padding: 0.42rem 0.6rem;
    border: 1px solid var(--water);
    color: var(--water);
    background: var(--water-soft);
    white-space: nowrap;
    font-weight: 500;
  }
  .tok.dim { border-color: var(--rule); color: var(--ink-3); background: transparent; }
  .tok b { font-weight: 700; }

  figcaption {
    margin-top: 1rem;
    color: var(--ink-3);
    font-size: 0.92rem;
    max-width: 62ch;
  }

  /* ---------------- shell ---------------- */

  .shell {
    max-width: 1180px;
    margin: 0 auto;
    padding: clamp(1.5rem, 3vw, 2.6rem) clamp(1.1rem, 3vw, 2.2rem) 5rem;
    display: grid;
    grid-template-columns: 210px minmax(0, 1fr);
    gap: clamp(1.5rem, 3vw, 3rem);
    align-items: start;
  }

  /* ---------------- rail ---------------- */

  .rail { position: sticky; top: 1.5rem; display: grid; gap: 0.9rem; }

  .meter {
    height: 3px;
    background: var(--rule-2);
    position: relative;
    overflow: hidden;
  }
  .meter i {
    position: absolute;
    inset: 0;
    background: var(--water);
    transform: scaleX(0);
    transform-origin: left center;
    transition: transform 0.3s ease;
  }

  .rail ol { list-style: none; margin: 0; padding: 0; display: grid; gap: 1px; }

  .rail button {
    width: 100%;
    text-align: left;
    background: none;
    border: 0;
    border-left: 2px solid var(--rule-2);
    padding: 0.42rem 0 0.42rem 0.7rem;
    color: var(--ink-3);
    font-family: "JetBrains Mono", monospace;
    font-size: 0.78rem;
    line-height: 1.35;
    cursor: pointer;
    display: flex;
    gap: 0.55rem;
    align-items: baseline;
  }
  .rail button:hover { color: var(--ink); }
  .rail button[aria-current="true"] { color: var(--ink); border-left-color: var(--water); }
  .rail button.done { color: var(--ink-3); border-left-color: var(--water); }
  .rail button.done .n::after { content: "\2713"; }
  .rail button.done .n span { display: none; }
  .rail .n { color: var(--water); width: 1.1rem; flex: none; font-variant-numeric: tabular-nums; }
  .rail button:focus-visible { outline: 2px solid var(--water); outline-offset: 2px; }

  /* ---------------- steps ---------------- */

  main { display: grid; gap: 1px; background: var(--rule-2); border-block: 1px solid var(--rule-2); }

  section.step { background: var(--paper); }

  .head {
    width: 100%;
    display: grid;
    grid-template-columns: 2.6rem minmax(0, 1fr) auto;
    gap: 0.9rem;
    align-items: baseline;
    background: none;
    border: 0;
    padding: 1.15rem 0.4rem;
    text-align: left;
    cursor: pointer;
    color: inherit;
    font: inherit;
  }
  .head:focus-visible { outline: 2px solid var(--water); outline-offset: -2px; }
  .head .idx {
    font-family: "JetBrains Mono", monospace;
    font-size: 0.78rem;
    color: var(--water);
    font-variant-numeric: tabular-nums;
    letter-spacing: 0.06em;
  }
  .head h2 { font-size: 1.22rem; line-height: 1.25; }
  .head .chev { color: var(--ink-3); font-family: "JetBrains Mono", monospace; font-size: 0.8rem; }
  section.step[data-open="true"] .chev { transform: rotate(180deg); }
  .chev { display: inline-block; transition: transform 0.18s ease; }

  .body { padding: 0 0.4rem 2rem; display: grid; gap: 1.4rem; }
  .body > p { margin: 0; max-width: 64ch; }
  .body > p.lede { font-size: 1.12rem; }
  section.step[data-open="false"] .body { display: none; }

  .where {
    font-family: "JetBrains Mono", monospace;
    font-size: 0.78rem;
    color: var(--ink-2);
    background: var(--paper-2);
    border-left: 2px solid var(--water);
    padding: 0.5rem 0.75rem;
    max-width: 64ch;
  }

  /* ---------------- annotated listing ---------------- */

  .listing {
    border: 1px solid var(--rule);
    background: var(--card);
  }
  .listing-cap {
    display: flex;
    justify-content: space-between;
    gap: 1rem;
    padding: 0.5rem 0.8rem;
    border-bottom: 1px solid var(--rule);
    background: var(--paper-2);
  }

  .line {
    display: grid;
    grid-template-columns: 2.4rem minmax(0, 1.05fr) minmax(0, 1fr);
    border-top: 1px solid var(--rule-2);
  }
  .line:first-of-type { border-top: 0; }
  .line > .ln {
    font-family: "JetBrains Mono", monospace;
    font-size: 0.72rem;
    color: var(--ink-3);
    text-align: right;
    padding: 0.55rem 0.6rem 0 0;
    font-variant-numeric: tabular-nums;
    user-select: none;
  }
  .line > pre {
    margin: 0;
    padding: 0.5rem 0.9rem 0.55rem 0;
    overflow-x: auto;
  }
  .line > pre code {
    font-size: 0.855rem;
    line-height: 1.55;
    color: var(--ink);
    white-space: pre;
  }
  .line > .note {
    margin: 0;
    padding: 0.5rem 0.9rem 0.7rem;
    font-size: 0.93rem;
    line-height: 1.5;
    color: var(--ink-2);
    border-left: 1px solid var(--rule-2);
  }
  .line.blank > pre code { min-height: 0.6rem; display: block; }
  .line.key { background: var(--water-soft); }
  .line.key > .note { color: var(--ink); }

  code .k  { color: var(--water); font-weight: 500; }
  code .s  { color: var(--ochre); }
  code .c  { color: var(--ink-3); font-style: italic; }

  /* ---------------- callouts ---------------- */

  .trap {
    border: 1px solid var(--ochre);
    background: var(--ochre-soft);
    padding: 0.95rem 1.1rem;
    display: grid;
    gap: 0.5rem;
    max-width: 68ch;
  }
  .trap .label { color: var(--ochre); }
  .trap p { margin: 0; }

  /* ---------------- terminal checkpoint ---------------- */

  .check { display: grid; gap: 0.75rem; max-width: 68ch; }

  .term {
    background: var(--term-bg);
    color: var(--term-ink);
    padding: 0.85rem 1rem;
    overflow-x: auto;
    font-family: "JetBrains Mono", monospace;
    font-size: 0.83rem;
    line-height: 1.65;
    border: 1px solid var(--rule);
  }
  .term .p { color: var(--water); }
  .term .o { color: #8FA0A0; }

  label.tick {
    display: flex;
    gap: 0.7rem;
    align-items: flex-start;
    cursor: pointer;
    border: 1px solid var(--rule);
    padding: 0.75rem 0.95rem;
    background: var(--card);
    font-size: 0.98rem;
  }
  label.tick:hover { border-color: var(--water); }
  label.tick input { margin: 0.28rem 0 0; accent-color: var(--water); width: 1rem; height: 1rem; flex: none; }
  label.tick:has(input:checked) { border-color: var(--water); background: var(--water-soft); }
  label.tick:has(input:focus-visible) { outline: 2px solid var(--water); outline-offset: 2px; }

  .turn {
    border-top: 1px solid var(--rule);
    padding-top: 0.9rem;
    max-width: 66ch;
    display: grid;
    gap: 0.4rem;
  }

  footer.end {
    max-width: 1180px;
    margin: 0 auto;
    padding: 0 clamp(1.1rem, 3vw, 2.2rem) 4rem;
    color: var(--ink-3);
    font-size: 0.95rem;
    max-width: 70ch;
  }

  .reset {
    background: none;
    border: 1px solid var(--rule);
    color: var(--ink-3);
    font-family: "JetBrains Mono", monospace;
    font-size: 0.72rem;
    padding: 0.35rem 0.6rem;
    cursor: pointer;
  }
  .reset:hover { color: var(--ink); border-color: var(--ink-3); }

  @media (max-width: 860px) {
    .shell { grid-template-columns: minmax(0, 1fr); }
    .rail { position: static; }
    .rail ol { grid-template-columns: repeat(auto-fill, minmax(150px, 1fr)); display: grid; }
    .line { grid-template-columns: 2.4rem minmax(0, 1fr); }
    .line > .note { grid-column: 2; border-left: 0; border-top: 1px dashed var(--rule-2); padding-top: 0.4rem; }
  }

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

/* ============ site chrome ============ */

img { max-width: 100%; height: auto; }

a { color: var(--water); text-underline-offset: 0.18em; }
a:focus-visible { outline: 2px solid var(--water); outline-offset: 2px; }

.skip {
  position: absolute;
  left: -9999px;
  background: var(--card);
  color: var(--ink);
  padding: 0.6rem 1rem;
  border: 1px solid var(--water);
  z-index: 20;
}
.skip:focus { left: 1rem; top: 1rem; }

nav.site {
  border-bottom: 1px solid var(--rule);
  background: var(--paper);
  position: sticky;
  top: 0;
  z-index: 10;
}
.site-inner {
  max-width: 1180px;
  margin: 0 auto;
  padding: 0.7rem clamp(1.1rem, 3vw, 2.2rem);
  display: flex;
  flex-wrap: wrap;
  gap: 0.6rem 1.4rem;
  align-items: baseline;
  justify-content: space-between;
}
.wordmark {
  font-family: "JetBrains Mono", monospace;
  font-size: 0.86rem;
  font-weight: 700;
  letter-spacing: 0.02em;
  color: var(--ink);
  text-decoration: none;
}
.wordmark span { color: var(--water); }
.site-links { display: flex; flex-wrap: wrap; gap: 0 1.2rem; }
.site-links a {
  font-family: "JetBrains Mono", monospace;
  font-size: 0.74rem;
  letter-spacing: 0.09em;
  text-transform: uppercase;
  color: var(--ink-3);
  text-decoration: none;
}
.site-links a:hover, .site-links a[aria-current="page"] { color: var(--ink); }

/* ============ index page ============ */

.wrap {
  max-width: 1180px;
  margin: 0 auto;
  padding: 0 clamp(1.1rem, 3vw, 2.2rem);
}

.hero {
  display: grid;
  gap: 1.4rem;
  padding: clamp(2.2rem, 6vw, 4.5rem) 0 clamp(1.8rem, 4vw, 3rem);
  border-bottom: 1px solid var(--rule);
}
.hero p { margin: 0; }

.two {
  display: grid;
  grid-template-columns: minmax(0, 1.15fr) minmax(0, 1fr);
  gap: clamp(1.5rem, 4vw, 3.5rem);
  align-items: start;
}
@media (max-width: 780px) { .two { grid-template-columns: minmax(0, 1fr); } }

.plan {
  padding: clamp(2rem, 5vw, 3.5rem) 0 4rem;
  display: grid;
  gap: 1.6rem;
}

ol.phases { list-style: none; margin: 0; padding: 0; display: grid; gap: 1px; background: var(--rule-2); border-block: 1px solid var(--rule-2); }

.phase {
  background: var(--paper);
  display: grid;
  grid-template-columns: 3.4rem minmax(0, 1fr) 9rem;
  gap: 1rem;
  align-items: baseline;
  padding: 1rem 0.4rem;
  text-decoration: none;
  color: inherit;
}
a.phase:hover { background: var(--card); }
a.phase:hover h3 { color: var(--water); }
.phase .num {
  font-family: "JetBrains Mono", monospace;
  font-size: 0.78rem;
  color: var(--water);
  font-variant-numeric: tabular-nums;
  letter-spacing: 0.06em;
}
.phase h3 { font-size: 1.08rem; line-height: 1.3; }
.phase p { margin: 0.25rem 0 0; color: var(--ink-2); font-size: 0.97rem; max-width: 60ch; }
.phase .state {
  font-family: "JetBrains Mono", monospace;
  font-size: 0.68rem;
  letter-spacing: 0.1em;
  text-transform: uppercase;
  text-align: right;
  white-space: nowrap;
}
.state.live { color: var(--water); }
.state.soon { color: var(--ink-3); }
.phase.pending { opacity: 0.62; }
.phase.pending .num { color: var(--ink-3); }

@media (max-width: 700px) {
  .phase { grid-template-columns: 2.6rem minmax(0, 1fr); }
  .phase .state { grid-column: 2; text-align: left; margin-top: 0.35rem; }
}

/* ============ prerequisites ============ */

.pre {
  border: 1px solid var(--rule);
  background: var(--card);
  padding: clamp(1rem, 2.5vw, 1.5rem);
  display: grid;
  gap: 0.85rem;
  max-width: 68ch;
}
.pre ul { margin: 0; padding-left: 1.1rem; display: grid; gap: 0.35rem; }
.pre p { margin: 0; }

/* ============ chapter footer nav ============ */

.chapnav {
  max-width: 1180px;
  margin: 0 auto;
  padding: 2rem clamp(1.1rem, 3vw, 2.2rem) 5rem;
  display: flex;
  flex-wrap: wrap;
  gap: 1rem;
  justify-content: space-between;
  border-top: 1px solid var(--rule);
}
.chapnav a {
  font-family: "JetBrains Mono", monospace;
  font-size: 0.8rem;
  text-decoration: none;
  display: grid;
  gap: 0.2rem;
  max-width: 22rem;
}
.chapnav a span { color: var(--ink-3); font-size: 0.68rem; letter-spacing: 0.1em; text-transform: uppercase; }
.chapnav a b { color: var(--ink); font-weight: 500; font-family: "Bricolage Grotesque", sans-serif; font-size: 1rem; }
.chapnav a:hover b { color: var(--water); }
.chapnav .next { text-align: right; margin-left: auto; }