/* --- Reset & Base --- */
*, *::before, *::after { box-sizing: border-box; margin: 0; padding: 0; }

:root {
  --bg: #fafaf8;
  --fg: #1a1a1a;
  --muted: #6b6b6b;
  --accent: #2d5a9e;
  --border: #ddd;
  --insight-bg: #f0f4fa;
  --insight-border: #b3c8e8;
  --fact-bg: #eef1f5;
  --given-bg: #e8e8e4;
  --font-body: 'Georgia', 'Times New Roman', serif;
  --font-mono: 'Menlo', 'Consolas', monospace;
  --font-math: 'Cambria Math', 'Latin Modern Math', 'Georgia', serif;
  --max-width: 640px;
}

html {
  font-size: 18px;
  scroll-behavior: smooth;
}

body {
  font-family: var(--font-body);
  color: var(--fg);
  background: var(--bg);
  line-height: 1.7;
  min-height: 100vh;
  display: flex;
  flex-direction: column;
  align-items: center;
}

/* --- Header (title + nav) --- */
#header {
  position: fixed;
  top: 0;
  left: 0;
  right: 0;
  background: var(--bg);
  border-bottom: 1px solid var(--border);
  z-index: 100;
}

.site-title {
  font-family: var(--font-body);
  font-size: 0.7rem;
  letter-spacing: 0.12em;
  text-transform: uppercase;
  color: var(--muted);
  text-align: center;
  padding: 0.5rem 0 0;
  margin: 0;
}

.site-title a {
  color: var(--muted);
  text-decoration: none;
}

.site-title a:hover {
  color: var(--fg);
}

.site-backlink {
  position: absolute;
  left: 1rem;
  bottom: 0.5rem;
  font-family: var(--font-body);
  font-size: 0.65rem;
  letter-spacing: 0.12em;
  text-transform: uppercase;
  color: var(--muted);
  text-decoration: none;
  opacity: 0.7;
}

.site-backlink:hover {
  color: var(--fg);
  opacity: 1;
}

/* --- Navigation --- */
#nav {
  display: flex;
  justify-content: center;
  gap: 1.5rem;
  padding: 0.4rem 0 0.5rem;
  font-family: var(--font-mono);
  font-size: 0.8rem;
}

#nav a {
  color: var(--muted);
  text-decoration: none;
  width: 1.8rem;
  height: 1.8rem;
  display: flex;
  align-items: center;
  justify-content: center;
  border-radius: 50%;
  transition: color 0.2s, background 0.2s;
}

#nav a:hover {
  color: var(--fg);
  background: var(--fact-bg);
}

#nav a.nav-current {
  color: var(--accent);
  font-weight: bold;
}

/* --- Main content --- */
main {
  max-width: var(--max-width);
  width: 100%;
  padding: 6rem 1.5rem 4rem;
}

.step { }

h1 {
  font-size: 1.6rem;
  font-weight: 600;
  margin-bottom: 2rem;
  letter-spacing: -0.01em;
  line-height: 1.3;
}

p {
  margin-bottom: 1.4rem;
}

var {
  font-family: var(--font-math);
  font-style: italic;
}

strong {
  font-weight: 600;
}

/* --- Sudoku grid --- */
.sudoku-example {
  display: flex;
  justify-content: center;
  margin: 2rem 0;
}

.sudoku {
  border-collapse: collapse;
}

.sudoku td {
  width: 3rem;
  height: 3rem;
  text-align: center;
  vertical-align: middle;
  font-family: var(--font-mono);
  font-size: 1.1rem;
  border: 1px solid var(--border);
  color: var(--muted);
}

.sudoku td.given {
  color: var(--fg);
  font-weight: 600;
}

.sudoku td.deduced {
  color: #1a7a3a;
  font-weight: 600;
  background: #e6f4ea;
}

/* 2×2 box borders */
.sudoku tr:nth-child(2) td { border-bottom-width: 2px; border-bottom-color: var(--fg); }
.sudoku td:nth-child(2) { border-right-width: 2px; border-right-color: var(--fg); }
.sudoku tr:first-child td { border-top-width: 2px; border-top-color: var(--fg); }
.sudoku tr:last-child td { border-bottom-width: 2px; border-bottom-color: var(--fg); }
.sudoku td:first-child { border-left-width: 2px; border-left-color: var(--fg); }
.sudoku td:last-child { border-right-width: 2px; border-right-color: var(--fg); }

/* --- Fact pills --- */
.facts {
  display: flex;
  flex-wrap: wrap;
  gap: 0.5rem;
  margin: 1.5rem 0;
  justify-content: center;
}

.facts-label {
  font-family: var(--font-math);
  font-size: 1rem;
  color: var(--fg);
  margin-right: 0.2rem;
}

.fact {
  font-family: var(--font-mono);
  font-size: 0.8rem;
  background: var(--fact-bg);
  padding: 0.3rem 0.7rem;
  border-radius: 4px;
  color: var(--fg);
}

.fact.deduced-fact {
  background: #e6f4ea;
  color: #1a7a3a;
  font-weight: 600;
}

/* --- Lattice interactive --- */
.lattice-interactive {
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: 1rem;
  margin: 1.5rem 0;
  padding: 1.2rem 0;
}

.lattice-interactive svg {
  display: block;
}

.lattice-edge {
  stroke: var(--border);
  stroke-width: 1.5;
}

.lattice-edge.path-highlight {
  stroke: var(--accent);
  stroke-width: 2;
  stroke-opacity: 0.4;
}

.lattice-node circle {
  fill: var(--bg);
  stroke: var(--border);
  stroke-width: 1.5;
  transition: fill 0.15s, stroke 0.15s;
}

.lattice-node text {
  font-family: var(--font-mono);
  font-size: 9px;
  fill: var(--fg);
  pointer-events: none;
}

.lattice-node:hover circle {
  stroke: var(--accent);
}

.lattice-node.selected circle {
  fill: #e8eef8;
  stroke: var(--accent);
  stroke-width: 2;
}

.lattice-node.is-meet circle {
  fill: #e6f4ea;
  stroke: #1a7a3a;
  stroke-width: 2.5;
}

.lattice-node.is-join circle {
  fill: #fef3e0;
  stroke: #c67700;
  stroke-width: 2.5;
}

.lattice-results {
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: 0.4rem;
  font-size: 0.9rem;
}

.lattice-legend {
  display: flex;
  align-items: center;
  gap: 0.3rem;
  font-family: var(--font-mono);
  font-size: 0.7rem;
  color: var(--muted);
}

.legend-dot {
  display: inline-block;
  width: 10px;
  height: 10px;
  border-radius: 50%;
}

.legend-selected { background: #e8eef8; border: 1.5px solid var(--accent); }
.legend-meet { background: #e6f4ea; border: 1.5px solid #1a7a3a; }
.legend-join { background: #fef3e0; border: 1.5px solid #c67700; }

.lattice-result-line {
  font-family: var(--font-math);
  font-size: 0.9rem;
}

.lattice-hint {
  font-size: 0.8rem;
  color: var(--muted);
}

/* --- Operation examples (join/meet) --- */
.operation-example {
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: 0.5rem;
  margin: 1.5rem 0;
  padding: 1.2rem 0;
}

.operand {
  width: 100%;
}

.operation-result {
  width: 100%;
  padding-top: 0.8rem;
  border-top: 1px solid var(--border);
}

.fact.shared-fact {
  background: #e8eef8;
  color: var(--accent);
}

.fact.unique-fact {
  background: var(--fact-bg);
  color: var(--muted);
}

/* --- Chain diagram --- */
.chain {
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: 0.3rem;
  margin: 2rem 0;
  font-family: var(--font-math);
  font-size: 1.1rem;
}

.chain-node {
  padding: 0.3rem 0;
}

.chain-node-a0 {
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: 0.3rem;
  font-family: var(--font-math);
}

.chain-facts {
  display: flex;
  flex-wrap: wrap;
  gap: 0.3rem;
  justify-content: center;
  max-width: 14rem;
}

.chain-node-expanded {
  display: flex;
  align-items: center;
  gap: 0.3rem;
  white-space: nowrap;
}

.chain-label {
  font-family: var(--font-math);
  font-size: 0.95rem;
}

.chain-edge {
  color: var(--muted);
  font-size: 0.9rem;
}

/* --- Interactive container --- */
.interactive-container {
  display: flex;
  align-items: flex-start;
  justify-content: center;
  gap: 2.5rem;
  margin: 2rem 0;
}

.interactive-grid-side {
  flex-shrink: 0;
}

.interactive-chain-side {
  position: relative;
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: 0.3rem;
  font-family: var(--font-math);
  font-size: 1.1rem;
  height: 10rem;
  overflow-y: scroll;
  scrollbar-width: none;
}

.interactive-chain-side::-webkit-scrollbar {
  display: none;
}

.interactive-chain-side::before {
  content: "";
  position: sticky;
  top: 0;
  flex-shrink: 0;
  width: 100%;
  height: 3rem;
  background: linear-gradient(to bottom, var(--bg), transparent);
  pointer-events: none;
  z-index: 1;
}

/* Interactive sudoku inputs */
.sudoku-interactive input {
  width: 100%;
  height: 100%;
  border: none;
  background: transparent;
  text-align: center;
  font-family: var(--font-mono);
  font-size: 1.1rem;
  color: var(--fg);
  outline: none;
  caret-color: var(--accent);
}

.sudoku-interactive input:focus {
  background: #f5f5f0;
}

.sudoku-interactive input.correct {
  color: #1a7a3a;
  font-weight: 600;
  background: #e6f4ea;
}

.sudoku-interactive input.wrong {
  background: #fde8e8;
  color: #c53030;
}

.sudoku-interactive input:disabled {
  cursor: default;
}

/* --- Interactive controls --- */
.interactive-controls {
  display: flex;
  justify-content: center;
  margin: 0.5rem 0 1.5rem;
}

.reset-btn {
  font-family: var(--font-mono);
  font-size: 0.75rem;
  color: var(--muted);
  background: none;
  border: 1px solid var(--border);
  border-radius: 4px;
  padding: 0.25rem 0.75rem;
  cursor: pointer;
  transition: color 0.2s, border-color 0.2s;
}

.reset-btn:hover {
  color: var(--fg);
  border-color: var(--fg);
}

/* --- Incomparable pair --- */
.incomparable {
  display: flex;
  align-items: center;
  justify-content: center;
  gap: 1.5rem;
  margin: 1.5rem 0;
}

.incomparable-side {
  display: flex;
  align-items: center;
}

.incomparable-gap {
  font-family: var(--font-math);
  font-size: 1.2rem;
  color: var(--muted);
}

/* --- Key insight box --- */
.key-insight {
  margin: 2.5rem 0;
  padding: 1.2rem 1.5rem;
  background: var(--insight-bg);
  border-left: 3px solid var(--insight-border);
  font-size: 0.95rem;
  line-height: 1.6;
}

/* --- Next page link --- */
.next-link {
  display: block;
  text-align: right;
  margin-top: 4rem;
  padding: 1rem 0;
  font-size: 1rem;
  color: var(--accent);
  text-decoration: none;
  border-top: 1px solid var(--border);
  transition: color 0.2s;
}

.next-link:hover {
  color: var(--fg);
}

/* --- Prev link --- */
.prev-link {
  display: block;
  text-align: left;
  margin-bottom: 2rem;
  font-size: 1rem;
  color: var(--accent);
  text-decoration: none;
  transition: color 0.2s;
}

.prev-link:hover {
  color: var(--fg);
}

/* --- Navigation footer (prev + next together) --- */
.nav-footer {
  display: flex;
  justify-content: space-between;
  margin-top: 4rem;
  padding: 1rem 0;
  border-top: 1px solid var(--border);
}

.nav-footer a {
  font-size: 1rem;
  color: var(--accent);
  text-decoration: none;
  transition: color 0.2s;
}

.nav-footer a:hover {
  color: var(--fg);
}

/* --- Math blocks --- */
.math-block {
  text-align: center;
  margin: 1.5rem 0;
  font-family: var(--font-math);
  font-size: 1.1rem;
}

/* --- Mini sudoku grid cell highlights --- */
.sudoku td.agree {
  color: var(--fg);
  font-weight: 600;
  background: #e8eef8;
}

.sudoku td.disagree {
  color: var(--muted);
}

/* --- Mini sudoku grids --- */
.sudoku-mini td {
  width: 1.8rem;
  height: 1.8rem;
  font-size: 0.8rem;
}

.example-grids-inline {
  display: flex;
  align-items: center;
  justify-content: center;
  gap: 0.5rem;
  margin: 0.5rem 0;
}

.example-grids-inline .comma {
  font-family: var(--font-math);
  font-size: 1.1rem;
  color: var(--muted);
}

/* --- Galois connection diagram --- */
.galois-diagram {
  display: flex;
  align-items: center;
  justify-content: center;
  gap: 1.5rem;
  margin: 2rem 0;
  font-family: var(--font-math);
  font-size: 1.1rem;
}

.galois-label {
  color: var(--fg);
}

.galois-svg {
  color: var(--muted);
  font-family: var(--font-math);
}

/* --- Definition lists --- */
.definition {
  margin: 1.5rem 0;
  padding-left: 1rem;
  border-left: 2px solid var(--border);
}

.definition dt {
  font-weight: 600;
  margin-top: 0.8rem;
}

.definition dt:first-child {
  margin-top: 0;
}

.definition dd {
  margin-left: 0;
  margin-bottom: 0.5rem;
  color: var(--muted);
  font-size: 0.95rem;
}

/* --- Lattice items list --- */
.lattice-items {
  margin: 1.5rem 0;
}

.lattice-items li {
  margin-bottom: 0.8rem;
  margin-left: 1.2rem;
}

/* --- Hierarchy diagram --- */
.hierarchy {
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: 0.5rem;
  margin: 2.5rem 0;
  font-family: var(--font-mono);
  font-size: 0.85rem;
}

.hierarchy-node {
  padding: 0.5rem 1.2rem;
  background: var(--fact-bg);
  border-radius: 4px;
  text-align: center;
}

.hierarchy-arrow {
  color: var(--muted);
  font-family: var(--font-math);
  font-size: 1rem;
}

.hierarchy-with-label {
  display: flex;
  align-items: stretch;
  justify-content: center;
  gap: 2rem;
  margin: 2.5rem 0;
}

.hierarchy-side-label {
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: space-between;
  font-family: var(--font-mono);
  font-size: 0.7rem;
  color: var(--muted);
  padding: 0.5rem 0;
}

.hierarchy-side-arrow {
  font-size: 1.2rem;
  flex: 1;
  display: flex;
  align-items: center;
}

/* --- Round-trip diagram (SVG) --- */
.round-trip-svg-container {
  display: flex;
  justify-content: center;
  margin: 1.5rem 0;
}

.round-trip-svg .rt-label {
  font-family: var(--font-mono);
  font-size: 9px;
  fill: var(--muted);
  letter-spacing: 0.05em;
}

.round-trip-svg .rt-box {
  fill: var(--fact-bg);
  stroke: none;
}

.round-trip-svg .rt-box-tight {
  fill: #e6f4ea;
  stroke: none;
}

.round-trip-svg .rt-text {
  font-family: var(--font-mono);
  font-size: 14px;
  fill: var(--fg);
}

.round-trip-svg .rt-text-tight {
  font-family: var(--font-mono);
  font-size: 14px;
  fill: #1a7a3a;
  font-weight: 600;
}

.round-trip-svg .rt-arrow-label {
  font-family: var(--font-math);
  font-size: 14px;
  font-style: italic;
  fill: var(--muted);
}

/* --- Galois interactive (step 5) --- */
.galois-interactive-container {
  margin: 1.5rem 0;
}

.galois-controls {
  display: flex;
  align-items: center;
  gap: 0.5rem;
  margin-bottom: 1rem;
  flex-wrap: wrap;
}

.galois-select {
  font-family: var(--font-mono);
  font-size: 0.8rem;
  padding: 0.25rem 0.5rem;
  border: 1px solid var(--border);
  border-radius: 4px;
  background: var(--bg);
  color: var(--fg);
}

.galois-btn {
  font-family: var(--font-mono);
  font-size: 0.8rem;
  color: var(--bg);
  background: var(--accent);
  border: none;
  border-radius: 4px;
  padding: 0.3rem 0.8rem;
  cursor: pointer;
  transition: opacity 0.2s;
}

.galois-btn:disabled {
  opacity: 0.4;
  cursor: default;
}

.galois-stage-label {
  font-family: var(--font-mono);
  font-size: 0.75rem;
  color: var(--muted);
}

.galois-panels {
  display: flex;
  align-items: flex-start;
  gap: 1.5rem;
  flex-wrap: wrap;
}

.galois-panel {
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: 0.5rem;
  min-height: 6rem;
}

.galois-panel-label {
  font-family: var(--font-mono);
  font-size: 0.75rem;
  color: var(--muted);
  letter-spacing: 0.05em;
  margin-bottom: 0.3rem;
}

.galois-pool {
  display: flex;
  flex-wrap: wrap;
  gap: 3px;
  max-width: 12rem;
}

.thumbnail-extra {
  outline: 2px solid #e8853d;
  outline-offset: -1px;
}

.galois-extra-note {
  font-family: var(--font-mono);
  font-size: 0.75rem;
  color: #e8853d;
  font-weight: 600;
  margin-top: 0.3rem;
}

.galois-invalid-note {
  font-family: var(--font-mono);
  font-size: 0.7rem;
  font-style: italic;
  color: var(--muted);
}

.sudoku-mini.grid-highlight {
  outline: 2px solid var(--accent);
  outline-offset: 2px;
}

.sudoku td.preview-cell {
  color: var(--muted);
  font-style: italic;
}

/* --- Side note --- */
.side-note {
  margin: 1.5rem 0;
  padding: 0.8rem 1.2rem;
  font-size: 0.85rem;
  color: var(--muted);
  border: 1px solid var(--border);
  border-radius: 4px;
}

/* --- Powerset interactive --- */
.powerset-interactive {
  display: flex;
  align-items: flex-start;
  gap: 2rem;
  margin: 2rem 0;
}

.powerset-left {
  flex-shrink: 0;
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: 0.5rem;
}

.powerset-count {
  font-family: var(--font-mono);
  font-size: 0.85rem;
  color: var(--muted);
}

.powerset-invalid {
  font-family: var(--font-mono);
  font-size: 0.75rem;
  font-style: italic;
  color: var(--muted);
}

.powerset-right {
  position: relative;
  flex: 1;
  min-width: 0;
  overflow: hidden;
}

.powerset-right.overflowing::after {
  content: "";
  position: absolute;
  bottom: 0;
  left: 0;
  right: 0;
  height: 3rem;
  background: linear-gradient(to bottom, transparent, var(--bg));
  pointer-events: none;
  z-index: 1;
}

#grid-pool {
  display: flex;
  flex-wrap: wrap;
  align-content: flex-start;
  gap: 3px;
  justify-content: flex-start;
  max-height: 24rem;
  overflow: hidden;
}


/* Thumbnail grids */
.thumbnail {
  border-collapse: collapse;
  transition: width 0.3s;
}

.thumbnail {
  cursor: pointer;
}

.thumbnail td {
  width: 6px; height: 6px; font-size: 0;
  padding: 0; border: none;
}

.thumbnail td[data-d="1"] { background: #2488cf; }
.thumbnail td[data-d="2"] { background: #f57c20; }
.thumbnail td[data-d="3"] { background: #3dab4a; }
.thumbnail td[data-d="4"] { background: #b44ec9; }

.thumbnail:not(.incompatible):hover {
  outline: 1.5px solid var(--fg);
}

.thumbnail.incompatible {
  opacity: 0.2;
  pointer-events: none;
  transition: opacity 0.3s;
}

/* Preview values shown on hover */
.sudoku-interactive input.preview {
  color: var(--muted);
  font-weight: 400;
  font-style: italic;
}

/* --- Hierarchy interactive (step 6) --- */
.hierarchy-interactive {
  display: flex;
  justify-content: center;
  align-items: flex-start;
  gap: 2rem;
  margin: 2rem 0;
}

.hierarchy-spacer {
  height: 2rem;
}

.hierarchy-col {
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: 0.5rem;
  min-width: 8rem;
}

.hierarchy-col-label {
  font-family: var(--font-mono);
  font-size: 0.7rem;
  color: var(--muted);
  text-align: center;
}

.hierarchy-thumbs {
  display: flex;
  align-items: center;
  gap: 3px;
}

.set-brace {
  font-family: var(--font-math);
  font-size: 1.4rem;
  color: var(--muted);
  line-height: 1;
}

.set-comma {
  font-family: var(--font-math);
  font-size: 1rem;
  color: var(--muted);
}

.hierarchy-preview {
  display: flex;
  align-items: center;
  justify-content: center;
}

.hierarchy-hint {
  font-family: var(--font-mono);
  font-size: 0.75rem;
  color: var(--muted);
  font-style: italic;
}

.sudoku td.empty-cell {
  background: var(--fact-bg);
  opacity: 0.4;
}

.sudoku td.pencil-cell {
  font-size: 0.55rem;
  color: var(--muted);
  font-family: var(--font-mono);
  letter-spacing: -0.02em;
}

/* --- Deduction lattice (step 7) --- */
.deduction-lattice-container {
  margin: 2rem 0;
  width: 100vw;
  position: relative;
  left: 50%;
  transform: translateX(-50%);
  max-width: 1200px;
}

.deduction-lattice-container svg {
  display: block;
  width: 100%;
  height: auto;
}

.lattice-level-label {
  font-family: var(--font-mono);
  font-size: 11px;
  fill: var(--muted);
}

.deduction-controls {
  display: flex;
  justify-content: center;
  gap: 1.5rem;
  margin: 1rem 0;
  flex-wrap: wrap;
}

.deduction-rule-label {
  font-family: var(--font-mono);
  font-size: 0.8rem;
  color: var(--fg);
  cursor: pointer;
  display: flex;
  align-items: center;
  gap: 0.3rem;
}

.deduction-rule-label input[type="checkbox"] {
  accent-color: #e05050;
}

/* --- To be continued --- */
.to-be-continued {
  text-align: center;
  font-family: var(--font-body);
  font-style: italic;
  font-size: 1.1rem;
  color: var(--muted);
  margin: 3rem 0 1rem;
}

/* --- Responsive --- */
@media (max-width: 600px) {
  html { font-size: 16px; }
  main { padding: 4.5rem 1rem 3rem; }
  .sudoku td { width: 2.5rem; height: 2.5rem; font-size: 1rem; }
  .site-backlink { position: static; display: block; text-align: center; padding-bottom: 0.4rem; }
}