/* Front Panel — Altair 8800
   The panel scales as one object: every dimension is in em, and the chassis
   font-size is the single fluid knob. Change that one clamp and the whole
   machine resizes without anything drifting out of alignment. */

:root {
  --page: #0b0e11;
  --page-raised: #141a20;
  --ink: #e7edf3;
  --ink-dim: #9aa7b4;
  --ink-faint: #8794a1;
  --rule: #232c35;
  --accent: #ff4b3e;
  --accent-cool: #6fb3d2;
  /* Button fill. The bright accent only reaches 3.3:1 against white. */
  --accent-solid: #d92e20;
  --accent-solid-hover: #c62a1d;

  --chassis-hi: #78838f;
  --chassis-lo: #454e58;
  --panel-hi: #3c4d5e;
  --panel-lo: #293743;
  --silkscreen: #eef3f8;

  --lamp-off: #401518;
  --lamp-rim: #1b0a0c;
  --lamp-on: 255, 62, 48;

  --chrome-hi: #eef1f4;
  --chrome-mid: #b9c0c8;
  --chrome-lo: #79828c;

  --font-ui: ui-sans-serif, system-ui, -apple-system, "Segoe UI", Roboto, Helvetica, Arial, sans-serif;
  --font-mono: ui-monospace, "SF Mono", "JetBrains Mono", Menlo, Consolas, monospace;
}

* { box-sizing: border-box; }

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

body {
  margin: 0;
  background: var(--page);
  color: var(--ink);
  font-family: var(--font-ui);
  line-height: 1.55;
  overflow-x: hidden;
}

a { color: var(--accent-cool); }
a:hover { color: #9fd0e6; }

.skip {
  position: absolute;
  left: -9999px;
}
.skip:focus {
  left: 1rem;
  top: 1rem;
  z-index: 10;
  background: var(--accent-solid);
  color: #fff;
  padding: 0.5rem 0.9rem;
  border-radius: 4px;
}

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

.masthead {
  max-width: 62rem;
  margin: 0 auto;
  padding: clamp(1.75rem, 5vw, 3.5rem) 1.25rem 1rem;
  text-align: center;
}

.masthead h1 {
  font-size: clamp(2rem, 7vw, 3.4rem);
  line-height: 1.03;
  margin: 0 0 0.5em;
  letter-spacing: -0.02em;
  font-weight: 650;
}

.standfirst {
  margin: 0 auto;
  max-width: 34em;
  color: var(--ink-dim);
  font-size: clamp(0.98rem, 2.1vw, 1.12rem);
  text-wrap: balance;
}

/* ---------- the machine ---------- */

.stage {
  padding: clamp(0.75rem, 2.5vw, 2rem) clamp(0.5rem, 2vw, 1.5rem) 0.5rem;
  display: flex;
  flex-direction: column;
  align-items: center;
}

.chassis {
  /* The one knob. Everything below is in em. */
  font-size: clamp(7.2px, 1.16vw, 13.5px);
  --col: 2.4em;
  --col-wide: 4em;
  width: 100%;
  max-width: 84em;
  padding: 1.2em 1.4em 1.6em;
  border-radius: 0.7em;
  background:
    linear-gradient(178deg, var(--chassis-hi), var(--chassis-lo) 55%, #3a424b);
  box-shadow:
    0 0.1em 0 rgba(255,255,255,0.28) inset,
    0 -0.25em 0.6em rgba(0,0,0,0.35) inset,
    0 1.6em 3.4em rgba(0,0,0,0.62);
  position: relative;
}

/* Brushed metal, cheap and convincing at this scale. */
.chassis::before {
  content: "";
  position: absolute;
  inset: 0;
  border-radius: inherit;
  pointer-events: none;
  opacity: 0.16;
  background: repeating-linear-gradient(
    92deg,
    rgba(255,255,255,0.5) 0 1px,
    rgba(0,0,0,0.28) 1px 2px
  );
  mix-blend-mode: overlay;
}

.chassis-head {
  display: flex;
  align-items: baseline;
  gap: 1.1em;
  padding: 0 0.2em 0.9em;
}

.brand-mits {
  font-weight: 800;
  font-size: 1.75em;
  letter-spacing: 0.16em;
  color: #f4f7fa;
  text-shadow: 0 1px 0 rgba(0,0,0,0.5);
}

.brand-model {
  font-size: 1.02em;
  letter-spacing: 0.34em;
  color: #dbe3ea;
  text-transform: uppercase;
  text-shadow: 0 1px 0 rgba(0,0,0,0.45);
}

.panel {
  background: linear-gradient(176deg, var(--panel-hi), var(--panel-lo));
  border-radius: 0.35em;
  padding: 1.5em 1.5em 1.35em;
  box-shadow:
    0 0 0 0.09em rgba(0,0,0,0.45),
    0 0.5em 1.4em rgba(0,0,0,0.4) inset;
}

/* ---------- lamps ---------- */

.lamp-deck { display: flex; flex-direction: column; gap: 1.5em; }

.lamp-row {
  display: flex;
  justify-content: space-between;
  align-items: flex-end;
  gap: 2em;
}

.lamp-left { display: flex; gap: 1.6em; }

.lamp-right {
  display: grid;
  grid-template-columns: repeat(16, var(--col));
  justify-content: end;
  gap: 0;
}

/* The DATA lamps are eight wide and share the right edge with ADDRESS, so
   D7..D0 land directly above A7..A0 — and above the data switches that
   write them. That vertical relationship is the whole point of the layout. */
.lamp-right.is-data { grid-template-columns: repeat(8, var(--col)); }

.lamp-group { position: relative; }

.lamp-group-label {
  position: absolute;
  top: -1.35em;
  left: 0;
  right: 0;
  text-align: center;
  font-size: 0.82em;
  letter-spacing: 0.28em;
  color: var(--silkscreen);
  opacity: 0.85;
  text-transform: uppercase;
}

.lamp-cell {
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: 0.42em;
  width: var(--col);
}

.lamp {
  width: 1.15em;
  height: 1.15em;
  border-radius: 50%;
  background:
    radial-gradient(circle at 34% 30%, rgba(255,255,255,0.22), transparent 55%),
    var(--lamp-off);
  box-shadow:
    0 0 0 0.16em var(--lamp-rim),
    0 0.06em 0.12em rgba(0,0,0,0.6) inset;
  position: relative;
}

/* --glow is written by the renderer, 0..1, from the bit's duty cycle. */
.lamp::after {
  content: "";
  position: absolute;
  inset: -0.06em;
  border-radius: 50%;
  opacity: var(--glow, 0);
  background: radial-gradient(circle at 40% 34%,
    rgba(255,235,232,0.98), rgba(var(--lamp-on), 0.98) 42%, rgba(var(--lamp-on), 0.5) 72%, transparent 88%);
  box-shadow:
    0 0 0.55em rgba(var(--lamp-on), 0.85),
    0 0 1.5em rgba(var(--lamp-on), 0.42);
}

.lamp-label {
  font-size: 0.76em;
  letter-spacing: 0.06em;
  color: var(--silkscreen);
  opacity: 0.82;
  white-space: nowrap;
}

/* ---------- switches ---------- */

.switch-deck {
  display: flex;
  justify-content: space-between;
  align-items: flex-start;
  gap: 2em;
  margin-top: 2.4em;
  padding-top: 1.5em;
  border-top: 0.09em solid rgba(0,0,0,0.28);
}

.switch-left { display: flex; gap: 0.35em; }

.switch-right-wrap { display: flex; flex-direction: column; }

/* Two banks of eight sit shoulder to shoulder and read as the original's
   single row of sixteen. On a phone they separate into the two halves people
   already name: sense switches and data switches. */
.switch-banks { display: flex; justify-content: flex-end; }

.switch-right {
  display: grid;
  grid-template-columns: repeat(8, var(--col));
  justify-content: end;
}

/* Octal reading grouping: extra air every three switches from A0 up. */
.switch-cell { position: relative; }
.switch-cell.octal-break::before {
  content: "";
  position: absolute;
  left: -0.06em;
  top: 1.4em;
  bottom: 1.4em;
  width: 0.09em;
  background: rgba(0,0,0,0.45);
  box-shadow: 0.09em 0 0 rgba(255,255,255,0.1);
}

.switch-cell {
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: 0.35em;
  width: var(--col);
  /* Touch target is deliberately larger than the visible switch. */
  padding: 0.5em 0;
  cursor: pointer;
  user-select: none;
  -webkit-tap-highlight-color: transparent;
  touch-action: manipulation;
}

.switch-cell.wide { width: var(--col-wide); }

.switch-caption-up,
.switch-caption-down {
  font-size: 0.7em;
  letter-spacing: 0.04em;
  color: var(--silkscreen);
  opacity: 0.8;
  text-align: center;
  line-height: 1.2;
  white-space: pre-line;
  display: flex;
  justify-content: center;
}
.switch-caption-up { min-height: 2.3em; align-items: flex-end; }
.switch-caption-down { min-height: 2.3em; align-items: flex-start; }

.switch-well {
  width: 1.5em;
  height: 2.5em;
  border-radius: 0.35em;
  background: linear-gradient(180deg, #1a222a, #2c3742);
  box-shadow: 0 0.08em 0.2em rgba(0,0,0,0.65) inset;
  display: flex;
  align-items: center;
  justify-content: center;
  position: relative;
}

.switch-paddle {
  width: 0.82em;
  height: 1.85em;
  border-radius: 0.42em;
  background: linear-gradient(96deg, var(--chrome-hi), var(--chrome-mid) 45%, var(--chrome-lo));
  box-shadow:
    0 0.1em 0.25em rgba(0,0,0,0.55),
    0 0 0 0.05em rgba(0,0,0,0.35);
  transform-origin: 50% 50%;
  transition: transform 90ms cubic-bezier(0.2, 0.9, 0.3, 1.4);
  transform: translateY(0.42em) scaleY(0.88);
}

.switch-cell[data-position="up"] .switch-paddle {
  transform: translateY(-0.42em) scaleY(0.88);
}
.switch-cell[data-position="center"] .switch-paddle {
  transform: translateY(0) scaleY(1);
}

.switch-cell:focus-visible { outline: 0.14em solid var(--accent-cool); outline-offset: 0.15em; border-radius: 0.3em; }

/* Guided mode points at the switch you need next. */
.switch-cell.is-called-out {
  border-radius: 0.3em;
  box-shadow: 0 0 0 0.12em var(--accent), 0 0 1.2em rgba(255,75,62,0.55);
  animation: callout 1.6s ease-in-out infinite;
}

@keyframes callout {
  0%, 100% { box-shadow: 0 0 0 0.12em var(--accent), 0 0 0.7em rgba(255,75,62,0.35); }
  50% { box-shadow: 0 0 0 0.12em var(--accent), 0 0 1.6em rgba(255,75,62,0.75); }
}

@media (prefers-reduced-motion: reduce) {
  .switch-cell.is-called-out { animation: none; }
}

.switch-cell.is-momentary .switch-well::after {
  content: "";
  position: absolute;
  inset: auto 0 -0.55em 0;
  height: 0.14em;
  background: rgba(255,255,255,0.25);
  border-radius: 1em;
}

/* Octal digit readout under each group of three data switches. */
.octal-readout {
  display: grid;
  grid-template-columns: repeat(16, var(--col));
  justify-content: end;
  margin-top: 0.5em;
}

.octal-digit {
  grid-column: span 3;
  align-self: center;
  text-align: center;
  font-family: var(--font-mono);
  font-size: 0.95em;
  color: var(--accent);
  opacity: 0.9;
}
.octal-digit:nth-child(1) { grid-column: 1 / span 1; }
.octal-digit:nth-child(2) { grid-column: 2 / span 3; }
.octal-digit:nth-child(3) { grid-column: 5 / span 3; }
.octal-digit:nth-child(4) { grid-column: 8 / span 3; }
.octal-digit:nth-child(5) { grid-column: 11 / span 3; }
.octal-digit:nth-child(6) { grid-column: 14 / span 3; }

.panel-hint {
  margin: 1.1rem 0 0;
  color: var(--ink-dim);
  font-size: 0.95rem;
  text-align: center;
  min-height: 1.5em;
}
.panel-hint b { color: var(--ink); }

/* ---------- narrow screens: split the address bank into its two real halves ---------- */

@media (max-width: 900px) {
  .chassis { font-size: clamp(9px, 2.6vw, 13px); }

  .lamp-row { flex-direction: column; align-items: stretch; gap: 1.6em; }
  .lamp-left { justify-content: center; }
  .lamp-right, .lamp-right.is-data { grid-template-columns: repeat(8, 1fr); justify-content: stretch; }

  .switch-deck { flex-direction: column-reverse; gap: 1.8em; }
  .switch-banks { flex-direction: column; gap: 1.4em; }
  .switch-bank { width: 100%; }
  .switch-right { grid-template-columns: repeat(8, 1fr); justify-content: stretch; }
  /* Ten status lamps will not fit in a row on a phone, so the eight true
     status lamps take an eight-wide grid and the two flag lamps centre. */
  .lamp-left.is-status { display: grid; grid-template-columns: repeat(8, 1fr); width: 100%; }
  .lamp-group.is-status { width: 100%; }
  .lamp-left { flex-wrap: wrap; justify-content: center; }
  .lamp-cell { width: auto; min-width: 2.4em; }
  /* The octal grouping does not line up with eight-bit banks, so read it as
     a plain octal number instead of trying to sit it under the switches. */
  .octal-readout { display: flex; justify-content: center; gap: 0.6em; }
  .octal-digit, .octal-digit:nth-child(n) { grid-column: auto; }
  .switch-left { flex-wrap: wrap; justify-content: center; gap: 0.5em 0.2em; }
  .switch-cell { width: auto; min-width: 2.9em; padding: 0.55em 0; }
  .switch-cell.wide { width: auto; min-width: 4.6em; }
  .switch-cell.octal-break { margin-left: 0; }
  .bank-label {
    font-size: 0.8em;
    letter-spacing: 0.2em;
    text-transform: uppercase;
    color: var(--silkscreen);
    opacity: 0.75;
    margin: 0 0 0.4em;
  }
}

@media (min-width: 901px) {
  .bank-label { display: none; }
}

/* ---------- console ---------- */

.console {
  max-width: 58rem;
  margin: clamp(1.5rem, 4vw, 3rem) auto 0;
  padding: 0 1.25rem 4rem;
}

.console-tabs {
  display: flex;
  gap: 0.35rem;
  border-bottom: 1px solid var(--rule);
  margin-bottom: 1.4rem;
  overflow-x: auto;
}

.tab {
  appearance: none;
  background: none;
  border: 0;
  border-bottom: 2px solid transparent;
  color: var(--ink-faint);
  font: inherit;
  font-size: 0.95rem;
  padding: 0.6rem 0.9rem;
  cursor: pointer;
  white-space: nowrap;
}
.tab:hover { color: var(--ink-dim); }
.tab.is-active { color: var(--ink); border-bottom-color: var(--accent); }

.tabpanel { display: none; }
.tabpanel.is-active { display: block; }

h2 { font-size: 1.35rem; margin: 0 0 0.6rem; letter-spacing: -0.01em; }
h3 { font-size: 1.02rem; margin: 1.8rem 0 0.5rem; letter-spacing: 0.01em; }
h3 small { color: var(--ink-faint); font-weight: 400; }
p { margin: 0 0 1rem; }

.btn {
  appearance: none;
  font: inherit;
  font-size: 0.95rem;
  padding: 0.6rem 1.1rem;
  border-radius: 0.4rem;
  border: 1px solid var(--rule);
  background: var(--page-raised);
  color: var(--ink);
  cursor: pointer;
  min-height: 2.75rem;
}
.btn:hover { border-color: #33404c; }
.btn:disabled { opacity: 0.4; cursor: default; }
.btn-primary { background: var(--accent-solid); border-color: var(--accent-solid); color: #fff; font-weight: 600; }
.btn-primary:hover { background: var(--accent-solid-hover); border-color: var(--accent-solid-hover); }
.btn-ghost { background: none; color: var(--ink-dim); }

/* guided mode */

.guide {
  background: var(--page-raised);
  border: 1px solid var(--rule);
  border-radius: 0.6rem;
  padding: 1.3rem;
}
.guide-head { display: flex; justify-content: space-between; align-items: baseline; gap: 1rem; }
.guide-head h2 { margin: 0; }
.guide-progress { color: var(--ink-faint); font-size: 0.85rem; margin: 0; font-variant-numeric: tabular-nums; }
.guide-body { margin: 0.9rem 0 1.2rem; font-size: 1.03rem; }
.guide-body b { color: #fff; }
.guide-body code {
  font-family: var(--font-mono);
  background: #0d1319;
  border: 1px solid var(--rule);
  border-radius: 0.25rem;
  padding: 0.08em 0.35em;
  font-size: 0.9em;
  color: var(--accent);
}
.guide-nav { display: flex; gap: 0.6rem; flex-wrap: wrap; }
.guide-foot { margin: 1.1rem 0 0; color: var(--ink-faint); font-size: 0.85rem; }

/* programs */

.program-picker { display: flex; flex-wrap: wrap; gap: 0.6rem; margin-bottom: 1.4rem; }

.program-card {
  flex: 1 1 14rem;
  text-align: left;
  padding: 0.9rem 1rem;
  border-radius: 0.5rem;
  border: 1px solid var(--rule);
  background: var(--page-raised);
  color: var(--ink);
  font: inherit;
  cursor: pointer;
}
.program-card:hover { border-color: #35424e; }
.program-card.is-active { border-color: var(--accent); }
.program-card b { display: block; margin-bottom: 0.2rem; }
.program-card span { color: var(--ink-faint); font-size: 0.85rem; }

.program-detail p { color: var(--ink-dim); }
.program-actions { display: flex; gap: 0.6rem; flex-wrap: wrap; margin: 1rem 0 1.4rem; }

.listing {
  width: 100%;
  border-collapse: collapse;
  font-family: var(--font-mono);
  font-size: 0.83rem;
  display: block;
  overflow-x: auto;
  white-space: nowrap;
}
.listing th {
  text-align: left;
  color: var(--ink-faint);
  font-weight: 500;
  border-bottom: 1px solid var(--rule);
  padding: 0.4rem 0.8rem 0.4rem 0;
}
.listing td { padding: 0.22rem 0.8rem 0.22rem 0; border-bottom: 1px solid #171e25; }
.listing .col-octal { color: var(--accent); }
.listing .col-comment { color: var(--ink-faint); white-space: normal; }

/* machine state */

.state-grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(7rem, 1fr));
  gap: 0.6rem;
  margin-bottom: 0.5rem;
}
.state-cell {
  background: var(--page-raised);
  border: 1px solid var(--rule);
  border-radius: 0.4rem;
  padding: 0.55rem 0.7rem;
}
.state-cell dt { color: var(--ink-faint); font-size: 0.75rem; letter-spacing: 0.06em; text-transform: uppercase; }
.state-cell dd { margin: 0.15rem 0 0; font-family: var(--font-mono); font-size: 1rem; }

.dump {
  background: #0d1319;
  border: 1px solid var(--rule);
  border-radius: 0.4rem;
  padding: 0.8rem;
  font-family: var(--font-mono);
  font-size: 0.78rem;
  overflow-x: auto;
  color: var(--ink-dim);
  margin: 0 0 1rem;
  max-height: 18rem;
}

.sources { color: var(--ink-dim); }
.colophon { color: var(--ink-faint); font-size: 0.9rem; margin-top: 2rem; }

.foot {
  border-top: 1px solid var(--rule);
  padding: 1.5rem 1.25rem 3rem;
  text-align: center;
  color: var(--ink-faint);
  font-size: 0.88rem;
}
.foot p { margin: 0; }

@media (prefers-reduced-motion: reduce) {
  .switch-paddle { transition: none; }
}

/* ══════════════════════════════════════════════════════════
   Reading layer: the chapters, the interactives, the teletype
   ══════════════════════════════════════════════════════════ */

.prose {
  max-width: 54rem;
  margin: 0 auto;
  padding: 0 1.25rem 5rem;
}

/* sticky section stepper */

.stepper {
  position: sticky;
  top: 0;
  z-index: 20;
  background: rgba(11, 14, 17, 0.92);
  backdrop-filter: blur(10px);
  border-bottom: 1px solid var(--rule);
  margin-top: 2rem;
}
.stepper ol {
  display: flex;
  gap: 0.15rem;
  list-style: none;
  margin: 0 auto;
  padding: 0 1rem;
  max-width: 66rem;
  overflow-x: auto;
  scrollbar-width: none;
}
.stepper ol::-webkit-scrollbar { display: none; }
.stepper a {
  display: block;
  white-space: nowrap;
  font-size: 0.82rem;
  color: var(--ink-faint);
  text-decoration: none;
  padding: 0.7rem 0.7rem;
  border-bottom: 2px solid transparent;
}
.stepper a::before {
  content: attr(data-step);
  display: inline-grid;
  place-items: center;
  width: 1.25rem;
  height: 1.25rem;
  margin-right: 0.4rem;
  border-radius: 50%;
  border: 1px solid currentColor;
  font-size: 0.68rem;
  vertical-align: -0.2rem;
}
.stepper a:hover { color: var(--ink-dim); }
.stepper a.is-current { color: var(--ink); border-bottom-color: var(--accent); }
.stepper a.is-current::before { background: var(--accent-solid); border-color: var(--accent-solid); color: #fff; }

/* chapters */

.chapter {
  padding: clamp(2.5rem, 6vw, 4.5rem) 0 0;
  scroll-margin-top: 4rem;
}
.chapter h2 {
  font-size: clamp(1.5rem, 4vw, 2.05rem);
  letter-spacing: -0.02em;
  margin: 0 0 1rem;
  line-height: 1.15;
  display: flex;
  align-items: baseline;
  gap: 0.7rem;
}
.chapter-num {
  flex: none;
  font-size: 0.78rem;
  font-variant-numeric: tabular-nums;
  color: var(--accent);
  border: 1px solid var(--accent);
  border-radius: 50%;
  width: 1.6rem;
  height: 1.6rem;
  display: inline-grid;
  place-items: center;
  transform: translateY(-0.15em);
}
.chapter h3 { font-size: 1.06rem; margin: 2rem 0 0.6rem; }
.chapter h4 { font-size: 0.95rem; margin: 1.5rem 0 0.5rem; color: var(--ink-dim); }
.chapter ul { color: var(--ink-dim); padding-left: 1.1rem; }
.chapter li { margin-bottom: 0.5rem; }

.lede {
  font-size: clamp(1.02rem, 2.4vw, 1.18rem);
  color: var(--ink);
  margin-bottom: 1.4rem;
  text-wrap: pretty;
}
.prose p { color: var(--ink-dim); }
.prose p b, .prose li b { color: var(--ink); }
.prose code {
  font-family: var(--font-mono);
  font-size: 0.88em;
  background: #0d1319;
  border: 1px solid var(--rule);
  border-radius: 0.25rem;
  padding: 0.08em 0.35em;
  color: var(--accent);
  white-space: nowrap;
}

.defs { display: grid; gap: 0.75rem; margin: 1.5rem 0; }
.def {
  background: var(--page-raised);
  border: 1px solid var(--rule);
  border-radius: 0.55rem;
  padding: 1rem 1.15rem;
}
.def > b { display: block; margin-bottom: 0.35rem; color: var(--ink); }
.def p { margin: 0; font-size: 0.95rem; }

.callout {
  border-left: 3px solid var(--accent);
  background: linear-gradient(90deg, rgba(255,75,62,0.08), transparent 60%);
  padding: 0.9rem 1.1rem;
  border-radius: 0 0.4rem 0.4rem 0;
  margin: 1.6rem 0;
  font-size: 0.97rem;
}

/* bit readout */

.readout {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(9rem, 1fr));
  gap: 0.6rem;
  margin: 1.4rem 0;
}
.readout-row {
  background: var(--page-raised);
  border: 1px solid var(--rule);
  border-radius: 0.5rem;
  padding: 0.7rem 0.9rem;
}
.readout-row span {
  display: block;
  font-size: 0.7rem;
  letter-spacing: 0.09em;
  text-transform: uppercase;
  color: var(--ink-faint);
}
.readout-row b {
  font-family: var(--font-mono);
  font-size: 1.25rem;
  color: var(--accent);
  letter-spacing: 0.04em;
}

/* instruction decoder */

.decoder {
  background: var(--page-raised);
  border: 1px solid var(--rule);
  border-radius: 0.6rem;
  padding: 1.1rem;
  margin: 1.4rem 0;
}
.decoder-bits { display: flex; gap: 0.6rem; flex-wrap: wrap; }
.bitgroup {
  flex: 1 1 6rem;
  text-align: center;
  background: #0d1319;
  border: 1px solid var(--rule);
  border-radius: 0.45rem;
  padding: 0.6rem 0.4rem;
}
.bitgroup b {
  display: block;
  font-family: var(--font-mono);
  font-size: 1.3rem;
  letter-spacing: 0.14em;
  color: var(--accent-cool);
}
.bitgroup span {
  font-size: 0.68rem;
  letter-spacing: 0.08em;
  text-transform: uppercase;
  color: var(--ink-faint);
}
.decoder-out { margin-top: 0.9rem; text-align: center; }
.decoder-mnemonic {
  font-family: var(--font-mono);
  font-size: clamp(1.3rem, 4.5vw, 1.8rem);
  color: var(--ink);
  letter-spacing: 0.03em;
}
.decoder-note { color: var(--ink-dim); font-size: 0.95rem; margin-top: 0.2rem; }
.decoder-extra { color: var(--ink-faint); font-size: 0.83rem; margin-top: 0.35rem; min-height: 1.2em; }

/* the 1976 split */

.split { display: grid; gap: 0.9rem; margin: 1.6rem 0; }
@media (min-width: 720px) { .split { grid-template-columns: 1fr 1fr; } }
.split-half {
  background: var(--page-raised);
  border: 1px solid var(--rule);
  border-radius: 0.6rem;
  padding: 1.1rem 1.2rem;
}
.split-half h3 { margin: 0 0 0.5rem; color: var(--accent); font-size: 0.85rem; letter-spacing: 0.1em; text-transform: uppercase; }
.split-half p { font-size: 0.95rem; }
.split-half blockquote {
  margin: 0.9rem 0;
  padding-left: 0.9rem;
  border-left: 2px solid var(--rule);
  color: var(--ink);
  font-style: italic;
}
.split-half blockquote.mono {
  font-family: var(--font-mono);
  font-style: normal;
  font-size: 0.84rem;
  line-height: 1.7;
  border-left-color: var(--accent);
  color: var(--ink-dim);
}
.split-half blockquote.mono b { color: var(--accent); }
.split-foot { font-size: 0.85rem; color: var(--ink-faint) !important; margin-bottom: 0 !important; }

/* teletype */

.tty-frame {
  margin: 1.5rem 0 1rem;
  border: 1px solid var(--rule);
  border-radius: 0.6rem;
  overflow: hidden;
  background: #0a0d10;
}
.tty-bar {
  display: flex;
  justify-content: space-between;
  align-items: center;
  gap: 1rem;
  padding: 0.5rem 0.85rem;
  background: var(--page-raised);
  border-bottom: 1px solid var(--rule);
  font-size: 0.75rem;
  letter-spacing: 0.06em;
  text-transform: uppercase;
  color: var(--ink-faint);
}
.tty-state { color: var(--ink-faint); }
.tty-frame:has(.tty.is-live) .tty-state { color: #7ddf9a; }

.tty {
  position: relative;
  background:
    radial-gradient(120% 100% at 50% 0%, rgba(255,176,64,0.05), transparent 70%),
    #07090b;
  padding: 0.9rem 1rem;
  cursor: text;
}
.tty-screen {
  margin: 0;
  font-family: var(--font-mono);
  font-size: clamp(0.72rem, 2.6vw, 0.85rem);
  line-height: 1.45;
  color: #ffb444;
  text-shadow: 0 0 6px rgba(255,150,40,0.45);
  white-space: pre-wrap;
  word-break: break-word;
  min-height: 15rem;
  max-height: 24rem;
  overflow-y: auto;
}
.tty-cursor { color: #ffb444; }
.tty.is-belled { animation: belled 120ms; }
@keyframes belled { 50% { background-color: rgba(255,180,68,0.12); } }

/* Real input element, positioned out of sight. It exists so tapping the
   teletype on a phone brings up the keyboard, which is the only way to type. */
.tty-input {
  position: absolute;
  opacity: 0;
  pointer-events: none;
  width: 1px;
  height: 1px;
  border: 0;
  padding: 0;
}

.tty-actions {
  display: flex;
  gap: 0.6rem;
  flex-wrap: wrap;
  padding: 0.85rem;
  background: var(--page-raised);
  border-top: 1px solid var(--rule);
}
.tty-hint { font-size: 0.92rem; }

/* back to top */

.totop {
  position: fixed;
  right: 1rem;
  bottom: 1rem;
  z-index: 30;
  width: 2.9rem;
  height: 2.9rem;
  border-radius: 50%;
  border: 1px solid var(--rule);
  background: var(--page-raised);
  color: var(--ink);
  font-size: 1.1rem;
  cursor: pointer;
  opacity: 0;
  pointer-events: none;
  transition: opacity 180ms;
}
.totop.is-shown { opacity: 1; pointer-events: auto; }
.totop:hover { border-color: var(--accent); }

@media (prefers-reduced-motion: reduce) {
  .totop { transition: none; }
  .tty.is-belled { animation: none; }
}

/* ══════════════════════════════════════════════════════════
   Hero routes, glossary, keyboard help
   ══════════════════════════════════════════════════════════ */

.h1-sub {
  display: block;
  font-size: clamp(0.82rem, 2.2vw, 1.05rem);
  font-weight: 400;
  letter-spacing: 0.02em;
  color: var(--ink-dim);
  margin-top: 0.5em;
}
.h1-sub em { color: var(--accent); font-style: normal; }

.claims {
  list-style: none;
  display: flex;
  flex-wrap: wrap;
  justify-content: center;
  gap: 0.4rem 1.4rem;
  margin: 1.4rem 0 0;
  padding: 0;
  font-size: 0.9rem;
  color: var(--ink-dim);
}
.claims li::before {
  content: "✓";
  color: var(--accent);
  margin-right: 0.4rem;
  font-weight: 700;
}

.paths { margin: 2rem auto 0; max-width: 46rem; }
.paths-q {
  margin: 0 0 0.7rem;
  font-size: 0.88rem;
  color: var(--ink-faint);
  letter-spacing: 0.03em;
}
.paths-row { display: grid; gap: 0.6rem; }
@media (min-width: 700px) { .paths-row { grid-template-columns: repeat(3, 1fr); } }

.path {
  text-align: left;
  font: inherit;
  color: var(--ink);
  background: var(--page-raised);
  border: 1px solid var(--rule);
  border-radius: 0.55rem;
  padding: 0.85rem 1rem;
  cursor: pointer;
}
.path:hover { border-color: #35424e; }
.path.is-active { border-color: var(--accent); }
.path b { display: block; font-size: 1rem; }
.path-time {
  display: block;
  font-size: 0.75rem;
  letter-spacing: 0.05em;
  text-transform: uppercase;
  color: var(--accent);
  margin: 0.1rem 0 0.4rem;
}
.path-desc { display: block; font-size: 0.87rem; color: var(--ink-dim); line-height: 1.5; }

.kbd-hint { margin: 1.6rem 0 0; font-size: 0.82rem; color: var(--ink-faint); }
kbd {
  font-family: var(--font-mono);
  font-size: 0.85em;
  border: 1px solid var(--rule);
  border-bottom-width: 2px;
  border-radius: 0.25rem;
  padding: 0.05em 0.4em;
  background: var(--page-raised);
  color: var(--ink);
}

/* glossary */

.glossary {
  display: grid;
  gap: 0.1rem 1.2rem;
  margin: 1.2rem 0 0;
}
@media (min-width: 640px) { .glossary { grid-template-columns: minmax(8rem, max-content) 1fr; } }
.glossary dt {
  font-weight: 600;
  color: var(--ink);
  padding: 0.55rem 0 0;
}
.glossary dd {
  margin: 0;
  color: var(--ink-dim);
  padding: 0.55rem 0;
  border-bottom: 1px solid #171e25;
  font-size: 0.95rem;
}
@media (max-width: 639px) {
  .glossary dt { border-top: 1px solid #171e25; }
  .glossary dd { border-bottom: 0; padding-top: 0.15rem; }
}

/* keyboard help */

.shortcuts {
  position: fixed;
  inset: 0;
  z-index: 60;
  display: grid;
  place-items: center;
  background: rgba(4, 6, 8, 0.78);
  backdrop-filter: blur(4px);
  padding: 1.25rem;
}
.shortcuts[hidden] { display: none; }
.shortcuts-card {
  background: var(--page-raised);
  border: 1px solid var(--rule);
  border-radius: 0.7rem;
  padding: 1.4rem;
  max-width: 26rem;
  width: 100%;
  max-height: 86vh;
  overflow-y: auto;
}
.shortcuts-card h2 { margin: 0 0 1rem; }
.shortcuts-card dl {
  display: grid;
  grid-template-columns: max-content 1fr;
  gap: 0.55rem 1rem;
  margin: 0 0 1.3rem;
  align-items: baseline;
}
.shortcuts-card dt { white-space: nowrap; }
.shortcuts-card dd { margin: 0; color: var(--ink-dim); font-size: 0.92rem; }

/* ── Hero density.
   The machine is the reason anyone is here, so the hero must not push it off
   the fold. On a phone the route cards collapse to their titles and the
   claims list drops to two tight columns, which recovers roughly 450px. */

@media (max-width: 700px) {
  .masthead { padding-top: 1.5rem; padding-bottom: 0.5rem; }
  .standfirst { font-size: 0.95rem; line-height: 1.45; }

  .claims {
    display: grid;
    grid-template-columns: 1fr 1fr;
    gap: 0.3rem 0.8rem;
    margin-top: 1rem;
    font-size: 0.78rem;
    text-align: left;
  }
  .claims li { display: flex; align-items: baseline; }

  .paths { margin-top: 1.2rem; }
  .paths-q { margin-bottom: 0.5rem; font-size: 0.8rem; }
  .paths-row { grid-template-columns: 1fr 1fr 1fr; gap: 0.4rem; }
  .path { padding: 0.6rem 0.5rem; text-align: center; }
  .path b { font-size: 0.85rem; line-height: 1.2; }
  .path-time { font-size: 0.62rem; letter-spacing: 0.03em; margin: 0.2rem 0 0; }
  .path-desc { display: none; }

  .kbd-hint { margin-top: 1rem; font-size: 0.75rem; }
  .stage { padding-top: 0.75rem; }
}

@media (min-width: 701px) {
  .masthead { padding-bottom: 0.5rem; }
}