/* ── Radon Transform: research notebook explainer ── */

:root {
  --paper: #f6f2e8;
  --paper-elev: #fbf8f0;
  --paper-deep: #ece6d4;
  --ink: #1b1814;
  --ink-2: #3a342a;
  --ink-3: #6b6354;
  --ink-4: #9d9479;
  --rule: #cfc7b1;
  --rule-soft: #e3dcc8;

  /* Two-color semantic system: image space vs parameter space */
  --image: oklch(0.42 0.12 250);     /* deep blue */
  --image-soft: oklch(0.42 0.12 250 / 0.12);
  --image-tint: oklch(0.92 0.04 250);
  --param: oklch(0.55 0.16 32);      /* vermillion */
  --param-soft: oklch(0.55 0.16 32 / 0.14);
  --param-tint: oklch(0.93 0.05 32);
  --accent: oklch(0.50 0.10 145);    /* sage, used sparingly */

  --serif: "Source Serif 4", "Source Serif Pro", "Iowan Old Style", Georgia, serif;
  --mono: "JetBrains Mono", "SF Mono", Menlo, monospace;

  --maxw: 1180px;
}

* { box-sizing: border-box; }
html, body { margin: 0; padding: 0; }
body {
  background: var(--paper);
  color: var(--ink);
  font-family: var(--serif);
  font-size: 18px;
  line-height: 1.55;
  font-feature-settings: "kern", "liga", "onum";
  -webkit-font-smoothing: antialiased;
}

/* ─── Paper texture: faint horizontal rule, like a notebook ─── */
.paper-bg {
  background-image:
    radial-gradient(ellipse 800px 400px at 50% -100px, oklch(0.95 0.03 80 / 0.6), transparent 60%),
    linear-gradient(var(--paper), var(--paper));
}

/* ─── Header / masthead ─── */
.masthead {
  max-width: var(--maxw);
  margin: 0 auto;
  padding: 64px 48px 24px;
  border-bottom: 1px solid var(--rule);
}
.masthead .eyebrow {
  font-family: var(--mono);
  font-size: 11px;
  letter-spacing: 0.16em;
  text-transform: uppercase;
  color: var(--ink-3);
  display: flex;
  justify-content: space-between;
  margin-bottom: 28px;
}
.masthead h1 {
  font-family: var(--serif);
  font-weight: 400;
  font-size: 56px;
  line-height: 1.04;
  letter-spacing: -0.02em;
  margin: 0 0 18px;
  font-feature-settings: "kern", "liga", "lnum";
}
.masthead h1 em { font-style: italic; color: var(--ink-2); }
.masthead .subtitle {
  font-size: 20px;
  color: var(--ink-2);
  max-width: 720px;
  margin: 0 0 32px;
  font-style: italic;
}
.masthead .meta {
  display: flex;
  gap: 32px;
  font-family: var(--mono);
  font-size: 12px;
  color: var(--ink-3);
  border-top: 1px solid var(--rule-soft);
  padding-top: 16px;
}
.masthead .meta .k { color: var(--ink-4); margin-right: 8px; }

/* ─── TOC ─── */
.toc {
  max-width: var(--maxw);
  margin: 0 auto;
  padding: 28px 48px;
  border-bottom: 1px solid var(--rule);
  display: grid;
  grid-template-columns: 140px 1fr;
  gap: 24px;
  align-items: start;
}
.toc .toc-label {
  font-family: var(--mono);
  font-size: 11px;
  letter-spacing: 0.16em;
  text-transform: uppercase;
  color: var(--ink-3);
  padding-top: 4px;
}
.toc ol {
  list-style: none;
  padding: 0;
  margin: 0;
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 4px 32px;
  font-family: var(--mono);
  font-size: 13px;
}
.toc ol li { display: flex; gap: 12px; }
.toc ol li .num { color: var(--ink-4); width: 24px; }
.toc ol li a { color: var(--ink-2); text-decoration: none; border-bottom: 1px dotted transparent; }
.toc ol li a:hover { border-bottom-color: var(--ink-3); }

/* ─── Sections ─── */
.sec {
  max-width: var(--maxw);
  margin: 0 auto;
  padding: 72px 48px;
  border-bottom: 1px solid var(--rule);
}
.sec-head {
  display: grid;
  grid-template-columns: 140px 1fr;
  gap: 24px;
  margin-bottom: 32px;
}
.sec-head .num {
  font-family: var(--mono);
  font-size: 11px;
  letter-spacing: 0.16em;
  text-transform: uppercase;
  color: var(--ink-3);
  padding-top: 14px;
  border-top: 1px solid var(--ink);
  align-self: start;
}
.sec-head h2 {
  font-family: var(--serif);
  font-weight: 400;
  font-size: 38px;
  line-height: 1.1;
  letter-spacing: -0.015em;
  margin: 0;
  padding-top: 8px;
}
.sec-head h2 em { font-style: italic; }

.sec-body {
  display: grid;
  grid-template-columns: 140px 1fr;
  gap: 24px;
}
.sec-body .sidenote {
  font-family: var(--mono);
  font-size: 11px;
  line-height: 1.55;
  color: var(--ink-3);
  letter-spacing: 0.02em;
  padding-top: 4px;
}
.sec-body .sidenote .label {
  text-transform: uppercase;
  letter-spacing: 0.16em;
  color: var(--ink-4);
  margin-bottom: 8px;
  display: block;
}

.prose { max-width: 720px; }
.prose p { margin: 0 0 16px; text-wrap: pretty; }
.prose p + p { text-indent: 1.4em; }
.prose .lede { font-size: 21px; line-height: 1.45; color: var(--ink-2); margin-bottom: 24px; }
.prose .lede + p { text-indent: 0; }
.prose strong { font-weight: 600; }
.prose em { font-style: italic; }
.prose code, .mono { font-family: var(--mono); font-size: 0.82em; background: var(--paper-deep); padding: 1px 5px; border-radius: 3px; }

.prose h3 {
  font-family: var(--serif);
  font-weight: 500;
  font-style: italic;
  font-size: 22px;
  margin: 32px 0 12px;
  color: var(--ink);
}

/* Inline coloured terms */
.tk-image { color: var(--image); font-weight: 500; }
.tk-param { color: var(--param); font-weight: 500; }

/* ─── Figures ─── */
.fig {
  margin: 32px 0;
  background: var(--paper-elev);
  border: 1px solid var(--rule);
  border-radius: 2px;
  position: relative;
}
.fig-head {
  display: flex;
  justify-content: space-between;
  align-items: baseline;
  padding: 14px 20px;
  border-bottom: 1px solid var(--rule-soft);
  font-family: var(--mono);
  font-size: 11px;
  letter-spacing: 0.1em;
  text-transform: uppercase;
  color: var(--ink-3);
}
.fig-head .fig-num { color: var(--ink); font-weight: 600; }
.fig-body { padding: 20px; }
.fig-caption {
  padding: 14px 20px;
  border-top: 1px solid var(--rule-soft);
  font-family: var(--serif);
  font-size: 14px;
  font-style: italic;
  color: var(--ink-2);
  line-height: 1.5;
}

/* Two-panel layout: image space || parameter space */
.panels {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 1px;
  background: var(--rule-soft);
  border: 1px solid var(--rule-soft);
}
.panel {
  background: var(--paper-elev);
  padding: 16px;
  position: relative;
}
.panel-label {
  font-family: var(--mono);
  font-size: 10px;
  letter-spacing: 0.14em;
  text-transform: uppercase;
  display: flex;
  justify-content: space-between;
  align-items: center;
  margin-bottom: 10px;
}
.panel-label .name { color: var(--ink-2); }
.panel-label .dim { color: var(--ink-4); }
.panel.image .name { color: var(--image); }
.panel.param .name { color: var(--param); }
.panel svg { display: block; width: 100%; height: auto; }
.panel canvas { display: block; max-width: 100%; height: auto; image-rendering: pixelated; }

/* Three-panel for advanced */
.panels-3 {
  display: grid;
  grid-template-columns: 1fr 1fr 1fr;
  gap: 1px;
  background: var(--rule-soft);
  border: 1px solid var(--rule-soft);
}

/* Controls strip */
.controls {
  display: flex;
  flex-wrap: wrap;
  gap: 8px;
  align-items: center;
  padding: 12px 16px;
  border-top: 1px solid var(--rule-soft);
  background: var(--paper-deep);
  font-family: var(--mono);
  font-size: 12px;
}
.controls .lbl { color: var(--ink-3); margin-right: 4px; }
.btn {
  font-family: var(--mono);
  font-size: 11px;
  letter-spacing: 0.04em;
  text-transform: uppercase;
  background: var(--paper);
  color: var(--ink-2);
  border: 1px solid var(--rule);
  padding: 6px 12px;
  border-radius: 2px;
  cursor: pointer;
  transition: background 0.12s;
}
.btn:hover { background: var(--paper-elev); border-color: var(--ink-4); }
.btn.primary { background: var(--ink); color: var(--paper); border-color: var(--ink); }
.btn.primary:hover { background: var(--ink-2); }
.btn.active { background: var(--param); color: var(--paper-elev); border-color: var(--param); }
.btn:disabled { opacity: 0.4; cursor: not-allowed; }

.chip {
  display: inline-flex;
  align-items: center;
  gap: 6px;
  font-family: var(--mono);
  font-size: 11px;
  color: var(--ink-3);
  padding: 3px 8px;
  background: var(--paper);
  border: 1px solid var(--rule);
  border-radius: 2px;
}
.chip .sw { width: 8px; height: 8px; border-radius: 1px; }

.range {
  -webkit-appearance: none;
  appearance: none;
  height: 2px;
  background: var(--rule);
  width: 140px;
  border-radius: 1px;
}
.range::-webkit-slider-thumb {
  -webkit-appearance: none;
  appearance: none;
  width: 12px; height: 12px;
  background: var(--ink);
  border-radius: 50%;
  cursor: pointer;
}
.range::-moz-range-thumb {
  width: 12px; height: 12px;
  background: var(--ink);
  border-radius: 50%;
  border: 0;
  cursor: pointer;
}

/* ─── Math display ─── */
.math {
  font-family: var(--mono);
  font-size: 15px;
  background: var(--paper-deep);
  border-left: 2px solid var(--ink-2);
  padding: 14px 18px;
  margin: 20px 0;
  letter-spacing: 0.02em;
  color: var(--ink);
  overflow-x: auto;
}
.math .annot { color: var(--ink-3); font-size: 12px; padding-left: 12px; }

/* ─── Marginalia callout ─── */
.callout {
  border: 1px solid var(--rule);
  background: var(--paper-elev);
  padding: 16px 18px;
  margin: 24px 0;
  font-size: 16px;
  color: var(--ink-2);
}
.callout .callout-label {
  font-family: var(--mono);
  font-size: 10px;
  letter-spacing: 0.16em;
  text-transform: uppercase;
  color: var(--param);
  margin-bottom: 8px;
}

/* ─── Tables (parameters by dimension) ─── */
.tbl {
  width: 100%;
  border-collapse: collapse;
  font-size: 14px;
  margin: 16px 0;
  font-family: var(--serif);
}
.tbl th, .tbl td {
  text-align: left;
  padding: 10px 14px;
  border-bottom: 1px solid var(--rule-soft);
}
.tbl thead th {
  font-family: var(--mono);
  font-size: 11px;
  letter-spacing: 0.1em;
  text-transform: uppercase;
  color: var(--ink-3);
  font-weight: 500;
  border-bottom: 1px solid var(--ink-2);
}
.tbl td.mono { font-family: var(--mono); font-size: 12px; }
.tbl tr:hover td { background: var(--paper-deep); }

/* ─── SVG common ─── */
.diagram-svg { font-family: var(--mono); font-size: 10px; }
.diagram-svg .axis { stroke: var(--ink-3); stroke-width: 1; }
.diagram-svg .axis-tick { stroke: var(--ink-4); stroke-width: 0.5; }
.diagram-svg .grid { stroke: var(--rule); stroke-width: 0.5; }
.diagram-svg .grid-major { stroke: var(--rule); stroke-width: 0.8; }
.diagram-svg .label { fill: var(--ink-3); font-size: 10px; }
.diagram-svg .label-axis { fill: var(--ink-2); font-style: italic; font-family: var(--serif); font-size: 13px; }
.diagram-svg .pt-image { fill: var(--image); stroke: var(--paper-elev); stroke-width: 1.5; }
.diagram-svg .pt-param { fill: var(--param); stroke: var(--paper-elev); stroke-width: 1.5; }
.diagram-svg .ln-image { stroke: var(--image); stroke-width: 1.5; fill: none; }
.diagram-svg .ln-param { stroke: var(--param); stroke-width: 1.2; fill: none; opacity: 0.78; }
.diagram-svg .ln-truth { stroke: var(--accent); stroke-width: 1.5; fill: none; stroke-dasharray: 4 3; }
.diagram-svg text { user-select: none; }

/* ─── Footer ─── */
.colo {
  max-width: var(--maxw);
  margin: 0 auto;
  padding: 48px;
  font-family: var(--mono);
  font-size: 11px;
  color: var(--ink-4);
  display: flex;
  justify-content: space-between;
  letter-spacing: 0.04em;
}

/* ─── Responsive ─── */
@media (max-width: 1100px) {
  .panels, .panels-3 { grid-template-columns: 1fr; }
}
@media (max-width: 900px) {
  .masthead, .toc, .sec { padding-left: 24px; padding-right: 24px; }
  .masthead h1 { font-size: 40px; }
  .sec-head, .sec-body, .toc { grid-template-columns: 1fr; }
  .sec-head .num { border-top: none; padding-top: 0; }
  .toc ol { grid-template-columns: 1fr; }
}