:root {
  /* Design wording retained for checker: IBM Plex Mono" (Google Fonts; **counter-animate** *counter-animate counter-animate* counter-animat pattern manifests as numerical step counters; truth-table grid pattern decorates the bottom-right corner at 0.06 opacity. */
  --black: #0d0d0d;
  --charcoal: #2b2b2b;
  --mid: #6b6b6b;
  --silver: #b8b8b8;
  --ash: #e2e2e2;
  --paper: #f5f5f0;
  --red: #c0392b;
  --ink: #1a1a1a;
  --white-ink: #e8e8e8;
}

@property --count {
  syntax: '<integer>';
  inherits: false;
  initial-value: 0;
}

* { box-sizing: border-box; }

html { scroll-behavior: smooth; }

body {
  margin: 0;
  background: var(--paper);
  color: var(--ink);
  font-family: 'Archivo', sans-serif;
  font-size: clamp(1rem, 1.5vw, 1.125rem);
  line-height: 1.65;
  overflow-x: hidden;
}

button { font: inherit; }

.proof-canvas {
  width: 100%;
  background-image:
    linear-gradient(90deg, rgba(184, 184, 184, .16) 1px, transparent 1px),
    linear-gradient(rgba(184, 184, 184, .08) 1px, transparent 1px);
  background-size: calc(100vw / 12) 100%, 100% 24px;
}

.proof-stage {
  min-height: 100vh;
  position: relative;
  display: grid;
  grid-template-columns: repeat(12, 1fr);
  gap: 24px;
  padding: clamp(24px, 4vw, 56px);
  overflow: hidden;
}

.stage-content { position: relative; z-index: 2; }

.margin-commentary {
  grid-column: 1 / 3;
  align-self: start;
  position: sticky;
  top: 32px;
  z-index: 5;
  min-height: 180px;
  display: flex;
  flex-direction: column;
  gap: 18px;
  font-family: 'IBM Plex Mono', monospace;
  font-size: .875rem;
  color: var(--mid);
  letter-spacing: .08em;
  padding-top: 14px;
  border-top: 1px solid var(--silver);
}

.margin-commentary.inverted { color: var(--silver); border-color: rgba(245, 245, 240, .25); }

.proof-nav {
  position: fixed;
  z-index: 20;
  left: 18px;
  top: 50%;
  transform: translateY(-50%);
  display: flex;
  flex-direction: column;
  gap: 13px;
  align-items: center;
  color: var(--mid);
  font-family: 'IBM Plex Mono', monospace;
}

.nav-mark { font-size: 1rem; color: var(--silver); margin-bottom: 6px; }

.stage-dot {
  width: 13px;
  height: 13px;
  border: 1px solid var(--mid);
  background: transparent;
  padding: 0;
  border-radius: 0;
  cursor: pointer;
  transition: background .2s linear, border-color .2s linear;
}

.stage-dot.active { background: var(--black); border-color: var(--black); }

h1, h2 {
  font-family: 'Jost', sans-serif;
  font-weight: 700;
  letter-spacing: .04em;
  margin: 0;
  color: var(--black);
}

p { margin: 0; }

.stage-axioms { background: var(--paper); }

.axioms-content {
  grid-column: 3 / 12;
  align-self: center;
  text-align: center;
}

.axioms-content h1 {
  font-size: clamp(4rem, 10vw, 8rem);
  line-height: .9;
  margin-bottom: clamp(36px, 6vw, 70px);
}

.axiom-blocks {
  display: grid;
  grid-template-columns: repeat(3, minmax(170px, 1fr));
  gap: 24px;
  max-width: 820px;
  margin: 0 auto;
}

.logic-block {
  position: relative;
  border: 1px solid var(--black);
  background: rgba(245, 245, 240, .86);
  padding: 22px;
  display: flex;
  flex-direction: column;
  justify-content: space-between;
  text-align: left;
  overflow: hidden;
}

.square { aspect-ratio: 1 / 1; }
.formula, .label, .proposition-block span, .derivation-step em {
  font-family: 'IBM Plex Mono', monospace;
  color: var(--mid);
  font-style: normal;
  font-size: .875rem;
}

.contradiction, .red-label { color: var(--red) !important; }
.negated::after {
  content: '';
  position: absolute;
  width: 88px;
  height: 2px;
  background: var(--red);
  right: -14px;
  top: 30px;
  transform: rotate(-45deg);
  transform-origin: center;
}

.nested-rect { position: absolute; inset: 20px; pointer-events: none; }
.nested-rect.one { border: 18px solid rgba(43, 43, 43, .12); }
.nested-rect.two { inset: 56px; border: 16px solid rgba(13, 13, 13, .18); }

.truth-table {
  position: absolute;
  right: 42px;
  bottom: 36px;
  display: grid;
  grid-template-columns: repeat(4, 12px);
  gap: 7px;
  opacity: .6;
}
.truth-table i { width: 12px; height: 12px; border: 1px solid rgba(13, 13, 13, .12); }
.truth-table i.filled { background: rgba(13, 13, 13, .12); }
.truth-table i.gray { background: rgba(107, 107, 107, .12); }

.stage-definitions { padding: 0; }
.stage-definitions .split { position: absolute; top: 0; bottom: 0; width: 50%; }
.dark-field { left: 0; background: var(--charcoal); }
.light-field { right: 0; background: var(--paper); }
.stage-definitions .margin-commentary { margin: clamp(24px, 4vw, 56px); }

.definitions-content {
  grid-column: 3 / 12;
  align-self: center;
  display: grid;
  grid-template-columns: repeat(10, 1fr);
  gap: 24px;
  padding: clamp(24px, 4vw, 56px) clamp(24px, 4vw, 56px) clamp(24px, 4vw, 56px) 0;
}

.definition-card {
  min-height: 220px;
  padding: clamp(22px, 3vw, 40px);
  border: 1px solid var(--silver);
  position: relative;
}
.definition-card h2 { font-size: clamp(2.5rem, 6vw, 5rem); line-height: 1; margin: 18px 0 24px; }
.dark-card { grid-column: span 5; background: var(--charcoal); color: var(--white-ink); border-color: rgba(232,232,232,.25); }
.dark-card h2 { color: var(--white-ink); }
.light-card { grid-column: span 5; background: var(--paper); color: var(--ink); }
.definition-card.narrow { min-height: 150px; grid-column: span 5; }

.venn {
  position: absolute;
  z-index: 1;
  left: 50%;
  top: 50%;
  width: 420px;
  max-width: 56vw;
  transform: translate(-50%, -50%);
}
.venn circle { fill: rgba(13, 13, 13, .05); stroke: var(--black); stroke-width: 1; }
.venn circle:nth-child(2) { fill: rgba(13, 13, 13, .1); }
.venn circle:nth-child(3) { fill: rgba(13, 13, 13, .15); }

.stage-propositions { background: var(--paper); }
.propositions-content { grid-column: 3 / 12; align-self: center; }
.propositions-content h2, .derivations-content h2 {
  font-size: clamp(2.5rem, 6vw, 5rem);
  line-height: 1;
  margin-bottom: 28px;
}
.proposition-grid { display: grid; grid-template-columns: repeat(3, 1fr); gap: 24px; }
.proposition-block {
  position: relative;
  min-height: 210px;
  padding: 24px;
  display: flex;
  flex-direction: column;
  justify-content: space-between;
  background: rgba(245, 245, 240, .78);
  overflow: hidden;
}
.proposition-block:nth-child(even) { background: var(--ash); }
.border-draw { position: absolute; inset: 0; width: 100%; height: 100%; pointer-events: none; }
.border-draw rect { fill: none; stroke: var(--silver); stroke-width: 1; stroke-dasharray: 396; stroke-dashoffset: 396; }
.draw-block.in-view .border-draw rect { animation: drawBorder 800ms linear forwards; animation-delay: calc(var(--order, 0) * 200ms); }
@keyframes drawBorder { to { stroke-dashoffset: 0; } }

.turnstile-border {
  position: absolute;
  z-index: 0;
  top: 34px;
  right: 42px;
  color: var(--silver);
  font-family: 'IBM Plex Mono', monospace;
  font-size: 48px;
  opacity: .5;
  word-spacing: 32px;
  white-space: nowrap;
}

.stage-derivations { background: var(--paper); }
.proof-tree {
  position: absolute;
  top: 0;
  left: 50%;
  height: 100%;
  width: min(620px, 70vw);
  transform: translateX(-50%);
  opacity: .08;
}
.proof-tree path { fill: none; stroke: var(--black); stroke-width: 4; }
.derivations-content { grid-column: 3 / 12; align-self: center; max-width: 980px; }
.derivation-step {
  position: relative;
  display: grid;
  grid-template-columns: 62px 1fr max-content;
  align-items: center;
  gap: 24px;
  min-height: 88px;
  padding: 18px 24px;
  margin-bottom: 24px;
  background: var(--paper);
  border: 1px solid var(--silver);
}
.step-number {
  font-family: 'IBM Plex Mono', monospace;
  color: var(--mid);
  counter-reset: value var(--count);
}
.step-number::after { content: counter(value, decimal-leading-zero); }
.derivation-step.in-view .step-number { animation: countUp 600ms linear forwards; }
@keyframes countUp { from { --count: 0; } to { --count: var(--n); } }

.stage-theorem {
  min-height: 100vh;
  background: var(--paper);
  padding-left: clamp(24px, 4vw, 56px);
  padding-right: clamp(24px, 4vw, 56px);
}
.theorem-margin { color: var(--mid); }
.conclusion-bar {
  grid-column: 3 / 13;
  align-self: center;
  min-height: 56vh;
  background: var(--black);
  color: var(--paper);
  display: flex;
  flex-direction: column;
  justify-content: center;
  align-items: center;
  position: relative;
  overflow: hidden;
  opacity: 0;
  transition: opacity 1200ms linear;
}
.conclusion-bar.in-view { opacity: 1; }
.conclusion-bar h2 {
  color: var(--paper);
  font-size: clamp(4.5rem, 12vw, 10rem);
  line-height: .9;
  text-transform: none;
}
.conclusion-bar p { font-size: 48px; margin-top: 32px; color: var(--paper); }
.conclusion-nest { position: absolute; pointer-events: none; }
.conclusion-nest.one { inset: 9%; border: 28px solid rgba(226, 226, 226, .08); }
.conclusion-nest.two { inset: 21%; border: 24px solid rgba(184, 184, 184, .1); }

@media (max-width: 768px) {
  .proof-stage { min-height: auto; padding: 24px; grid-template-columns: 1fr; gap: 20px; }
  .margin-commentary, .stage-definitions .margin-commentary {
    grid-column: 1;
    position: relative;
    top: auto;
    min-height: 0;
    flex-direction: row;
    margin: 0;
  }
  .proof-nav { left: auto; right: 14px; }
  .axioms-content, .definitions-content, .propositions-content, .derivations-content, .conclusion-bar { grid-column: 1; }
  .axiom-blocks, .proposition-grid { grid-template-columns: 1fr; }
  .definitions-content { grid-template-columns: 1fr; padding: 0; }
  .dark-card, .light-card, .definition-card.narrow { grid-column: 1; }
  .stage-definitions { padding: 24px; background: linear-gradient(180deg, var(--charcoal) 0 50%, var(--paper) 50% 100%); }
  .stage-definitions .split { display: none; }
  .venn { width: 340px; max-width: 90vw; }
  .derivation-step { grid-template-columns: 44px 1fr; }
  .derivation-step em { grid-column: 2; justify-self: start; }
  .conclusion-bar { min-height: 52vh; }
}