:root {
  --bg: #efebe3;
  --paper: #f7f4ec;
  --paper-2: #f3efe6;
  --ink: #1c1712;
  --ink-soft: #5e574e;
  --rule: #d6cfc2;
  --rule-strong: #b9b09f;
  --copper: #c45c2a;
  --copper-deep: #9a3f18;
  --copper-wash: #f0d8cc;
  --high: #c45c2a;
  --low: #b3ab9d;
  --sum: #243d32;
  --sum-wash: #d7e2db;
  --warn: #8a3728;
  --shadow: 0 18px 40px rgba(28, 23, 18, 0.06);
  --serif: "Fraunces", "Iowan Old Style", "Palatino Linotype", serif;
  --sans: "Manrope", "Avenir Next", "Segoe UI", sans-serif;
  --mono: "IBM Plex Mono", "ui-monospace", monospace;
  --radius: 2px;
}

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

html {
  scroll-behavior: smooth;
}

body {
  margin: 0;
  min-height: 100vh;
  background: var(--bg);
  color: var(--ink);
  font-family: var(--sans);
  font-size: 16px;
  line-height: 1.5;
  letter-spacing: -0.011em;
}

.grain {
  pointer-events: none;
  position: fixed;
  inset: 0;
  z-index: 8;
  opacity: 0.045;
  background-image: url("data:image/svg+xml,%3Csvg viewBox='0 0 180 180' xmlns='http://www.w3.org/2000/svg'%3E%3Cfilter id='n'%3E%3CfeTurbulence type='fractalNoise' baseFrequency='0.8' numOctaves='4' stitchTiles='stitch'/%3E%3C/filter%3E%3Crect width='100%25' height='100%25' filter='url(%23n)'/%3E%3C/svg%3E");
}

.skip {
  position: absolute;
  left: 16px;
  top: -40px;
  z-index: 20;
  padding: 8px 12px;
  background: var(--ink);
  color: var(--paper);
  text-decoration: none;
}

.skip:focus {
  top: 16px;
}

.page {
  width: min(1120px, calc(100% - 32px));
  margin: 0 auto;
  padding: 48px 0 80px;
}

.masthead {
  padding: 12px 0 36px;
  border-bottom: 1px solid var(--rule);
}

.masthead-meta {
  display: flex;
  justify-content: space-between;
  gap: 16px;
}

.kicker {
  margin: 0;
  font-family: var(--mono);
  font-size: 11px;
  font-weight: 500;
  letter-spacing: 0.16em;
  text-transform: uppercase;
  color: var(--ink-soft);
}

h1 {
  margin: 28px 0 12px;
  font-family: var(--serif);
  font-optical-sizing: auto;
  font-size: clamp(48px, 8vw, 88px);
  font-weight: 620;
  letter-spacing: -0.03em;
  line-height: 0.92;
}

.lede {
  margin: 0;
  max-width: 46ch;
  color: var(--ink-soft);
  font-size: 17px;
}

.panel {
  margin-top: 28px;
  padding: 28px 28px 24px;
  background: var(--paper);
  border: 1px solid var(--rule);
  box-shadow: var(--shadow);
}

.panel-head {
  display: flex;
  justify-content: space-between;
  align-items: flex-end;
  gap: 16px;
  margin-bottom: 22px;
}

.panel-head h2,
.explain h2 {
  margin: 0 0 4px;
  font-family: var(--serif);
  font-size: 28px;
  font-weight: 620;
  letter-spacing: -0.02em;
}

.panel-head p {
  margin: 0;
  color: var(--ink-soft);
  font-size: 14px;
}

.operand-row {
  display: grid;
  grid-template-columns: 56px minmax(0, 1fr) minmax(180px, 220px);
  gap: 20px;
  align-items: center;
  padding: 14px 0;
}

.operand-row + .operand-row {
  border-top: 1px dashed var(--rule);
}

.operand-row.sum-row {
  margin-top: 8px;
  padding-top: 20px;
  border-top: 1px solid var(--ink);
}

.op-letter {
  flex-shrink: 0;
  font-family: var(--serif);
  font-size: 34px;
  font-weight: 620;
  line-height: 1;
}

.op-letter sub {
  font-family: var(--mono);
  font-size: 12px;
  font-weight: 500;
}

.bits {
  display: flex;
  flex-wrap: nowrap;
  justify-content: flex-end;
  gap: 8px;
  min-width: 0;
}

.bit {
  position: relative;
  flex: 1 1 0;
  width: 72px;
  max-width: 72px;
  min-width: 0;
  height: 92px;
  padding: 0;
  overflow: hidden;
  border: 1px solid var(--rule-strong);
  background: var(--paper-2);
  color: var(--low);
  font-family: var(--mono);
  cursor: pointer;
  touch-action: manipulation;
  transition: background 0.18s ease, color 0.18s ease, border-color 0.18s ease, transform 0.12s ease;
}

.bit .place {
  position: absolute;
  top: 8px;
  left: 0;
  right: 0;
  font-size: 10px;
  letter-spacing: 0.12em;
  text-transform: uppercase;
  color: var(--ink-soft);
}

.bit .val {
  display: block;
  margin-top: 18px;
  font-size: 38px;
  font-weight: 500;
  line-height: 1.2;
}

.bit.on {
  background: var(--ink);
  border-color: var(--ink);
  color: var(--paper);
}

.bit.on .place {
  color: rgba(247, 244, 236, 0.62);
}

.bit:hover {
  transform: translateY(-1px);
}

.bit:focus-visible {
  outline: 2px solid var(--copper);
  outline-offset: 3px;
}

.bit[disabled] {
  cursor: default;
  transform: none;
}

.bit.sum {
  background: var(--paper);
}

.bit.sum.on {
  background: var(--sum);
  border-color: var(--sum);
  color: var(--paper);
}

.bit.carry-out {
  border-style: dashed;
}

.stepper {
  display: flex;
  align-items: center;
  justify-content: flex-end;
  gap: 8px;
}

.stepper button {
  width: 36px;
  height: 36px;
  border: 1px solid var(--rule-strong);
  background: transparent;
  color: var(--ink);
  font-size: 20px;
  line-height: 1;
  cursor: pointer;
}

.stepper button:hover:not(:disabled) {
  background: var(--ink);
  color: var(--paper);
}

.stepper button:disabled {
  opacity: 0.35;
  cursor: default;
}

.stepper button:focus-visible,
.chip:focus-visible,
.btn-trace:focus-visible {
  outline: 2px solid var(--copper);
  outline-offset: 2px;
}

.stepper input {
  width: 64px;
  border: none;
  border-bottom: 1px solid var(--ink);
  background: transparent;
  color: var(--ink);
  font-family: var(--serif);
  font-size: 32px;
  font-weight: 620;
  text-align: center;
  appearance: textfield;
  -moz-appearance: textfield;
}

.stepper input::-webkit-outer-spin-button,
.stepper input::-webkit-inner-spin-button {
  margin: 0;
  appearance: none;
  -webkit-appearance: none;
}

.stepper input:focus {
  outline: none;
  border-bottom-color: var(--copper);
}

.stepper .word {
  min-width: 5.5ch;
  color: var(--ink-soft);
  font-size: 13px;
}

.presets {
  display: flex;
  flex-wrap: wrap;
  align-items: center;
  gap: 8px;
  margin-top: 18px;
  padding-top: 16px;
  border-top: 1px solid var(--rule);
}

.presets-label {
  margin-right: 6px;
  font-family: var(--mono);
  font-size: 11px;
  letter-spacing: 0.14em;
  text-transform: uppercase;
  color: var(--ink-soft);
}

.chip {
  padding: 6px 12px;
  border: 1px solid var(--rule-strong);
  background: transparent;
  color: var(--ink);
  font-family: var(--mono);
  font-size: 12px;
  cursor: pointer;
}

.chip:hover,
.chip.active {
  background: var(--ink);
  color: var(--paper);
  border-color: var(--ink);
}

.hero-sum {
  margin-top: 28px;
  padding: 8px 4px 4px;
}

.hero-kicker {
  margin: 0 0 8px;
  font-family: var(--mono);
  font-size: 11px;
  letter-spacing: 0.16em;
  text-transform: uppercase;
  color: var(--ink-soft);
}

.hero-eq {
  margin: 0;
  font-family: var(--serif);
  font-size: clamp(36px, 6vw, 64px);
  font-weight: 620;
  letter-spacing: -0.03em;
  line-height: 1;
}

.hero-eq .plus,
.hero-eq .eq {
  color: var(--ink-soft);
  font-weight: 500;
}

.hero-eq .sum {
  color: var(--copper-deep);
}

.hero-words {
  margin: 10px 0 0;
  font-family: var(--mono);
  font-size: 13px;
  color: var(--ink-soft);
}

.column-mount {
  overflow-x: auto;
}

.column {
  display: grid;
  justify-content: end;
  gap: 0;
  font-family: var(--mono);
  width: max-content;
  margin-left: auto;
  margin-right: 8px;
}

.column-row {
  display: grid;
  grid-template-columns: 36px repeat(5, 52px);
  align-items: center;
  min-height: 44px;
}

.column-row.places .cell {
  font-size: 10px;
  letter-spacing: 0.08em;
  text-transform: uppercase;
  color: var(--ink-soft);
}

.column-row.carries .cell {
  font-size: 13px;
  color: var(--copper);
}

.column-row.total {
  border-top: 1px solid var(--ink);
  min-height: 56px;
  font-size: 22px;
}

.cell {
  text-align: center;
}

.cell.op {
  text-align: right;
  color: var(--ink-soft);
}

.cell.on {
  color: var(--ink);
  font-weight: 600;
}

.btn-trace {
  flex-shrink: 0;
  padding: 10px 16px;
  border: 1px solid var(--ink);
  background: var(--ink);
  color: var(--paper);
  font-family: var(--sans);
  font-size: 13px;
  font-weight: 600;
  letter-spacing: 0.02em;
  cursor: pointer;
}

.btn-trace:hover {
  background: var(--copper-deep);
  border-color: var(--copper-deep);
}

.btn-trace:disabled {
  opacity: 0.55;
  cursor: wait;
}

.legend {
  display: flex;
  flex-wrap: wrap;
  gap: 16px 22px;
  margin: -6px 0 16px;
  font-family: var(--mono);
  font-size: 11px;
  letter-spacing: 0.08em;
  text-transform: uppercase;
  color: var(--ink-soft);
}

.swatch {
  display: inline-block;
  width: 18px;
  height: 3px;
  margin-right: 8px;
  vertical-align: middle;
  background: var(--low);
}

.swatch.high {
  background: var(--copper);
}

.swatch.selected {
  height: 10px;
  border: 1.5px solid var(--copper);
  background: var(--copper-wash);
}

.circuit-scroll {
  overflow-x: auto;
  padding-bottom: 6px;
}

svg.schematic {
  display: block;
  width: 100%;
  min-width: 860px;
  height: auto;
}

svg.detail {
  min-width: 720px;
}

.wire {
  fill: none;
  stroke: var(--low);
  stroke-width: 2;
  stroke-linecap: square;
  stroke-linejoin: miter;
  transition: stroke 0.2s ease;
}

.wire.high {
  stroke: var(--high);
}

.wire.flow {
  stroke-dasharray: 5 7;
  animation: flow 0.7s linear infinite;
}

.gate-body {
  fill: var(--paper);
  stroke: var(--ink);
  stroke-width: 1.6;
}

.gate-body.high {
  fill: var(--copper-wash);
  stroke: var(--copper-deep);
}

.fa-hit {
  cursor: pointer;
}

.module {
  fill: var(--paper);
  stroke: var(--rule-strong);
  stroke-width: 1.4;
  cursor: pointer;
}

.module.selected {
  fill: #fbf3ee;
  stroke: var(--copper);
  stroke-width: 2;
}

.module:hover {
  stroke: var(--ink);
}

.pin-dot {
  stroke: var(--ink);
  stroke-width: 1.2;
}

.pin-dot.high {
  fill: var(--high);
  stroke: var(--copper-deep);
}

.pin-dot.low {
  fill: var(--paper);
  stroke: var(--low);
}

.label {
  font-family: var(--mono);
  font-size: 11px;
  fill: var(--ink-soft);
}

.label.ink {
  fill: var(--ink);
}

.bit-value {
  font-family: var(--mono);
  font-size: 13px;
  font-weight: 600;
  fill: var(--ink);
}

.place-tag {
  margin: 0;
  font-family: var(--mono);
  font-size: 12px;
  letter-spacing: 0.08em;
  text-transform: uppercase;
  color: var(--copper-deep);
}

.detail-grid {
  display: grid;
  grid-template-columns: 1fr minmax(220px, 280px);
  gap: 20px;
  align-items: start;
}

.equations {
  padding: 16px 16px 8px;
  border-left: 1px solid var(--rule);
}

.eq-block {
  margin-bottom: 18px;
}

.eq-block h3 {
  margin: 0 0 8px;
  font-family: var(--mono);
  font-size: 11px;
  font-weight: 500;
  letter-spacing: 0.14em;
  text-transform: uppercase;
  color: var(--ink-soft);
}

.eq-block p {
  margin: 0 0 6px;
  font-family: var(--mono);
  font-size: 13px;
  line-height: 1.55;
}

.eq-block .live {
  color: var(--copper-deep);
  font-weight: 600;
}

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

.signal-list li {
  display: flex;
  justify-content: space-between;
  gap: 12px;
  padding: 6px 0;
  border-bottom: 1px solid var(--rule);
  font-family: var(--mono);
  font-size: 12px;
}

.signal-list .v {
  font-weight: 600;
}

.signal-list .v.one {
  color: var(--copper-deep);
}

.explain {
  background: transparent;
  border: none;
  box-shadow: none;
  padding: 36px 4px 0;
}

.explain-grid {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  gap: 24px;
  margin-top: 18px;
}

.explain article h3 {
  margin: 0 0 8px;
  font-family: var(--serif);
  font-size: 22px;
  font-weight: 620;
}

.explain article p {
  margin: 0 0 10px;
  color: var(--ink-soft);
  font-size: 15px;
}

.mono-note {
  font-family: var(--mono) !important;
  font-size: 12px !important;
  color: var(--ink) !important;
}

.colophon {
  margin-top: 48px;
  padding-top: 16px;
  border-top: 1px solid var(--rule);
  color: var(--ink-soft);
  font-family: var(--mono);
  font-size: 11px;
  letter-spacing: 0.08em;
  text-transform: uppercase;
}

@keyframes flow {
  to {
    stroke-dashoffset: -24;
  }
}

@media (max-width: 860px) {
  .page {
    width: min(100% - 20px, 1120px);
    padding-top: 28px;
  }

  .panel {
    padding: 20px 16px 16px;
  }

  .operand-row {
    grid-template-columns: 40px 1fr;
    gap: 10px 12px;
  }

  .stepper {
    grid-column: 1 / -1;
    justify-content: flex-start;
    padding-left: 52px;
  }

  .bit {
    width: auto;
    max-width: 64px;
    height: 78px;
  }

  .bit .val {
    font-size: 28px;
  }

  svg.detail {
    min-width: 0;
  }

  .circuit-panel .circuit-scroll::after {
    content: "Swipe to see every full adder →";
    display: block;
    margin-top: 8px;
    font-family: var(--mono);
    font-size: 11px;
    letter-spacing: 0.08em;
    text-transform: uppercase;
    color: var(--ink-soft);
  }

  .detail-grid,
  .explain-grid {
    grid-template-columns: 1fr;
  }

  .equations {
    border-left: none;
    border-top: 1px solid var(--rule);
    padding: 16px 0 0;
  }

  .panel-head {
    flex-direction: column;
    align-items: flex-start;
  }
}

@media (prefers-reduced-motion: reduce) {
  html {
    scroll-behavior: auto;
  }

  .bit,
  .wire {
    transition: none;
  }

  .wire.flow {
    animation: none;
  }
}