:root {
  --bg: #EEF1F0;
  --ink: #20242B;
  --accent: #1B8073;
  --accent-soft: #E4F1EE;
  --result: #D9572C;
  --result-soft: #FBE9E1;
  --muted: #5B6168;
  --line: #C7CDC9;
  --white: #FFFFFF;

  --font-display: 'Space Grotesk', sans-serif;
  --font-body: 'IBM Plex Sans', sans-serif;
  --font-mono: 'IBM Plex Mono', monospace;
}

* { box-sizing: border-box; }

body {
  margin: 0;
  background: var(--bg);
  color: var(--ink);
  font-family: var(--font-body);
}

.site-header {
  padding: 2.5rem 1.5rem 1rem;
  text-align: center;
}

.wordmark {
  font-family: var(--font-display);
  font-weight: 700;
  font-size: 1.75rem;
  letter-spacing: -0.01em;
}

.tagline {
  margin: 0.4rem auto 0;
  max-width: 32rem;
  color: var(--muted);
  font-size: 0.98rem;
}

main {
  max-width: 800px;
  margin: 0 auto;
  padding: 0 1.5rem 4rem;
}

/* ── Diagram type toggle ──────────────────────────────────────────────── */

.diagram-toggle {
  display: flex;
  justify-content: center;
  gap: 0.5rem;
  margin-bottom: 1.75rem;
}

.toggle-btn {
  font-family: var(--font-body);
  font-weight: 500;
  font-size: 0.92rem;
  padding: 0.55rem 1.1rem;
  border: 1.5px solid var(--line);
  border-radius: 999px;
  background: var(--white);
  color: var(--muted);
  cursor: pointer;
  transition: border-color 0.15s, color 0.15s, background 0.15s;
}

.toggle-btn:hover { border-color: var(--accent); color: var(--accent); }

.toggle-btn.is-active {
  background: var(--accent);
  border-color: var(--accent);
  color: var(--white);
}

/* ── Panels ───────────────────────────────────────────────────────────── */

.diagram-panel { display: none; }
.diagram-panel.is-active { display: block; }

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

.control {
  display: flex;
  align-items: center;
  gap: 0.5rem;
  font-size: 0.85rem;
  color: var(--muted);
}

.control select {
  font-family: var(--font-mono);
  font-size: 0.9rem;
  padding: 0.25rem 0.5rem;
  border: 1.5px solid var(--line);
  border-radius: 6px;
  background: var(--white);
  color: var(--ink);
}

.leg-count-control #pretzel-leg-count {
  font-family: var(--font-mono);
  font-weight: 600;
  min-width: 1.2rem;
  text-align: center;
}

.step-btn {
  width: 1.6rem;
  height: 1.6rem;
  border-radius: 50%;
  border: 1.5px solid var(--accent);
  background: var(--white);
  color: var(--accent);
  font-size: 1rem;
  line-height: 1;
  cursor: pointer;
}

.step-btn:hover { background: var(--accent-soft); }
.step-btn:disabled { opacity: 0.35; cursor: not-allowed; }

/* ── Diagram stage ────────────────────────────────────────────────────── */

.diagram-stage {
  position: relative;
  background: var(--white);
  border: 1.5px solid var(--line);
  border-radius: 14px;
  margin: 0 auto;
  overflow: visible;
}

#pretzel-stage { width: 600px; height: 420px; }
#twovertex-stage { width: 700px; height: 380px; }

.diagram-stage svg { display: block; }

.diagram-stage line, .diagram-stage circle {
  stroke: var(--ink);
}

/* Leg / bridge input chips — the signature interaction: parameters are
   annotated directly on the diagram, not in a separate form below it. */
.leg-chip {
  position: absolute;
  display: flex;
  gap: 2px;
  transform: translate(-50%, -50%);
}

.leg-chip input {
  width: 2.5rem;
  text-align: center;
  font-family: var(--font-mono);
  font-weight: 600;
  font-size: 0.95rem;
  color: var(--accent);
  background: var(--accent-soft);
  border: 1.5px solid var(--accent);
  border-radius: 6px;
  padding: 0.2rem 0.1rem;
}

.leg-chip input:focus {
  outline: none;
  border-color: var(--ink);
}

.bridge-chip input {
  width: 2.5rem;
}

/* ── Compute + result ─────────────────────────────────────────────────── */

.compute-btn {
  display: block;
  margin: 1.5rem auto 0;
  font-family: var(--font-body);
  font-weight: 500;
  font-size: 0.95rem;
  padding: 0.65rem 1.8rem;
  border: none;
  border-radius: 999px;
  background: var(--ink);
  color: var(--white);
  cursor: pointer;
}

.compute-btn:hover { background: var(--accent); }
.compute-btn:disabled { opacity: 0.5; cursor: wait; }

.result-panel {
  margin-top: 1.5rem;
  padding: 1.25rem 1.5rem;
  border-radius: 12px;
  background: var(--white);
  border: 1.5px solid var(--line);
}

.result-panel + .result-panel {
  margin-top: 0.75rem;
}

.result-panel.identification:not(.is-muted):not(.is-error) {
  background: var(--result-soft);
  border-color: var(--result);
}

.result-panel .knot-name {
  font-family: var(--font-mono);
  font-weight: 600;
  font-size: 1.4rem;
  color: var(--result);
}

.result-panel .poly {
  margin-top: 0.5rem;
  font-family: var(--font-mono);
  font-size: 0.85rem;
  color: var(--ink);
  word-break: break-word;
}

.result-panel.is-error {
  background: #FCEEEE;
  border-color: #B43B3B;
  color: #B43B3B;
  font-family: var(--font-mono);
  font-size: 0.9rem;
}

.result-panel .panel-label {
  font-family: var(--font-mono);
  font-size: 0.7rem;
  letter-spacing: 0.06em;
  text-transform: uppercase;
  color: var(--muted);
  margin-bottom: 0.35rem;
}

/* ── Polynomial format toggle (inside the invariant panel) ──────────────── */
.result-panel .panel-label-row {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 0.75rem;
  margin-bottom: 0.35rem;
}
.result-panel .panel-label-row .panel-label { margin-bottom: 0; }

.poly-toggle { display: flex; gap: 0.25rem; }

.poly-toggle-btn {
  font-family: var(--font-mono);
  font-size: 0.62rem;
  letter-spacing: 0.04em;
  text-transform: uppercase;
  padding: 0.15rem 0.5rem;
  border: 1.5px solid var(--line);
  border-radius: 999px;
  background: var(--white);
  color: var(--muted);
  cursor: pointer;
}
.poly-toggle-btn:hover { border-color: var(--accent); color: var(--accent); }
.poly-toggle-btn.is-active {
  background: var(--accent);
  border-color: var(--accent);
  color: var(--white);
}

.result-panel.is-muted {
  background: var(--bg);
  border-color: var(--line);
}

.result-panel.is-muted .knot-name {
  color: var(--muted);
}

.result-panel .note {
  margin-top: 0.4rem;
  font-size: 0.82rem;
  color: var(--muted);
}

@media (max-width: 650px) {
  #pretzel-stage, #twovertex-stage { width: 100%; }
}

/* ── Cite corner button ───────────────────────────────────────────────── */

.cite-corner {
  position: fixed;
  top: 1rem;
  right: 1rem;
  z-index: 10;
  font-family: var(--font-body);
  font-size: 0.8rem;
  font-weight: 500;
  text-decoration: none;
  padding: 0.45rem 0.9rem;
  border-radius: 999px;
  border: 1.5px solid var(--accent);
  background: var(--white);
  color: var(--accent);
  box-shadow: 0 1px 3px rgba(0, 0, 0, 0.06);
  transition: background 0.15s, color 0.15s;
}

.cite-corner span { font-weight: 700; }
.cite-corner:hover { background: var(--accent); color: var(--white); }

/* ── Home / back nav link ─────────────────────────────────────────────── */

.home-link {
  display: inline-block;
  margin-bottom: 0.6rem;
  font-family: var(--font-mono);
  font-size: 0.8rem;
  color: var(--accent);
  text-decoration: none;
}

.home-link:hover { text-decoration: underline; }

/* ── Determinant row (in the invariant panel) ─────────────────────────── */

.det-row {
  display: flex;
  align-items: baseline;
  gap: 0.6rem;
  margin-top: 0.9rem;
  padding-top: 0.75rem;
  border-top: 1px solid var(--line);
}

.det-label {
  font-family: var(--font-mono);
  font-size: 0.7rem;
  letter-spacing: 0.06em;
  text-transform: uppercase;
  color: var(--muted);
}

.det-value {
  font-family: var(--font-mono);
  font-weight: 600;
  font-size: 1.1rem;
  color: var(--ink);
}

/* ── Home page ────────────────────────────────────────────────────────── */

.home-main { max-width: 720px; }

.home-hero {
  text-align: center;
  padding: 0.5rem 0 2rem;
  border-bottom: 1.5px solid var(--line);
  margin-bottom: 2rem;
}

.home-hero .lead {
  font-size: 1.1rem;
  line-height: 1.6;
  color: var(--ink);
  max-width: 40rem;
  margin: 0 auto 1.75rem;
}

.cta-btn {
  display: inline-block;
  font-family: var(--font-body);
  font-weight: 500;
  font-size: 0.98rem;
  text-decoration: none;
  padding: 0.7rem 1.6rem;
  border-radius: 999px;
  background: var(--ink);
  color: var(--white);
  transition: background 0.15s;
}

.cta-btn:hover { background: var(--accent); }

.home-section { margin-bottom: 2.5rem; }

.home-section h2 {
  font-family: var(--font-display);
  font-weight: 700;
  font-size: 1.25rem;
  margin: 0 0 1.1rem;
}

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

.home-steps li {
  display: flex;
  gap: 1rem;
  align-items: flex-start;
  margin-bottom: 1.1rem;
}

.step-num {
  flex: 0 0 auto;
  width: 1.9rem;
  height: 1.9rem;
  display: grid;
  place-items: center;
  border-radius: 50%;
  background: var(--accent-soft);
  color: var(--accent);
  font-family: var(--font-mono);
  font-weight: 600;
  font-size: 0.9rem;
}

.home-steps h3 {
  font-family: var(--font-body);
  font-weight: 500;
  font-size: 1rem;
  margin: 0.2rem 0 0.25rem;
}

.home-steps p, .home-list li {
  color: var(--muted);
  font-size: 0.95rem;
  line-height: 1.55;
  margin: 0;
}

.home-list { padding-left: 1.1rem; }
.home-list li { margin-bottom: 0.5rem; }

.mono { font-family: var(--font-mono); }

.home-footer-cta {
  text-align: center;
  padding-top: 1rem;
}

/* ── Cite page ────────────────────────────────────────────────────────── */

.cite-main { max-width: 720px; }

.cite-block {
  background: var(--white);
  border: 1.5px solid var(--line);
  border-radius: 12px;
  padding: 1.25rem 1.5rem;
  margin-bottom: 1.25rem;
}

.cite-block-label {
  font-family: var(--font-mono);
  font-size: 0.7rem;
  letter-spacing: 0.06em;
  text-transform: uppercase;
  color: var(--muted);
  margin-bottom: 0.6rem;
}

.cite-note { text-transform: none; letter-spacing: 0; }

.cite-text {
  margin: 0;
  line-height: 1.6;
  color: var(--ink);
}

.cite-fill {
  font-family: var(--font-mono);
  color: var(--muted);
}

.cite-bibtex {
  margin: 0;
  padding: 1rem 1.15rem;
  background: var(--bg);
  border: 1px solid var(--line);
  border-radius: 8px;
  overflow-x: auto;
  font-family: var(--font-mono);
  font-size: 0.85rem;
  line-height: 1.5;
  color: var(--ink);
}

.copy-btn {
  margin-top: 0.9rem;
  font-family: var(--font-body);
  font-size: 0.85rem;
  padding: 0.4rem 1rem;
  border-radius: 999px;
  border: 1.5px solid var(--accent);
  background: var(--white);
  color: var(--accent);
  cursor: pointer;
}

.copy-btn:hover { background: var(--accent-soft); }

/* ── Candidate list (mutants / multiple database matches) ─────────────── */
/* A polynomial invariant is not a complete invariant: distinct knots can
   share one invariant. When the lookup returns several entries we list them
   all rather than presenting the first as a unique identification. */

.result-panel .candidates {
  margin-top: 0.8rem;
  padding-top: 0.7rem;
  border-top: 1px solid var(--line);
}

.candidates-label {
  font-family: var(--font-mono);
  font-size: 0.7rem;
  letter-spacing: 0.06em;
  text-transform: uppercase;
  color: var(--muted);
  margin-bottom: 0.4rem;
}

.candidate-list {
  margin: 0;
  padding-left: 1.1rem;
  list-style: disc;
}

.candidate-list li {
  font-family: var(--font-mono);
  font-size: 0.95rem;
  color: var(--result);
  line-height: 1.5;
}

/* ── Knot diagram images (KnotInfo) ──────────────────────────────────────
   Shown inside the identification panel beneath the knot name. Usually one
   tile (the primary match); several when the invariant is ambiguous and more
   than one candidate has a diagram on file. Append to the end of style.css. */

.result-panel .knot-diagrams {
  display: flex;
  flex-wrap: wrap;
  gap: 0.9rem;
  margin-top: 0.9rem;
  padding-top: 0.8rem;
  border-top: 1px solid var(--line);
}

.result-panel .knot-diagram {
  margin: 0;
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: 0.35rem;
}

.result-panel .knot-diagram img {
  display: block;
  width: 132px;
  height: 132px;
  object-fit: contain;
  background: var(--white);
  border: 1.5px solid var(--line);
  border-radius: 10px;
  padding: 0.4rem;
}

.result-panel .knot-diagram figcaption {
  font-family: var(--font-mono);
  font-size: 0.78rem;
  color: var(--muted);
}