:root {
  --bg-top: #eef6ff;
  --bg-bottom: #d7e8ff;
  --panel: rgba(255, 255, 255, 0.82);
  --panel-border: rgba(18, 57, 99, 0.12);
  --ink: #15304d;
  --muted: #55708d;
  --accent: #0f766e;
  --shadow: 0 24px 60px rgba(19, 48, 77, 0.14);
}

* { box-sizing: border-box; }

body {
  margin: 0;
  min-height: 100vh;
  font-family: "Trebuchet MS", "Gill Sans", "Segoe UI", sans-serif;
  color: var(--ink);
  background:
    radial-gradient(circle at top left, rgba(255,255,255,0.85), transparent 30%),
    linear-gradient(180deg, var(--bg-top), var(--bg-bottom));
}

.page {
  width: min(1280px, calc(100% - 2rem));
  margin: 0 auto;
  padding: 1.5rem 0 2rem;
}

.hero { display: flex; align-items: flex-end; gap: 1rem; margin-bottom: 1rem; }
.hero-link {
  display: inline-flex; align-items: center; gap: 0.4rem;
  margin-bottom: 0.75rem; padding: 0.45rem 0.8rem;
  border-radius: 999px; text-decoration: none;
  font-size: 0.9rem; font-weight: 700; color: var(--ink);
  background: rgba(255,255,255,0.9); border: 1px solid rgba(21,48,77,0.12);
}
.hero-link:hover { background: white; }
.eyebrow { margin: 0 0 0.35rem; color: var(--accent); font-size: 0.9rem; font-weight: 700; letter-spacing: 0.08em; text-transform: uppercase; }
h1 { margin: 0; font-size: clamp(1.8rem, 4vw, 3rem); line-height: 0.95; }
.intro { max-width: 68ch; margin: 0.6rem 0 0; color: var(--muted); font-size: 1rem; }

.layout {
  display: grid;
  grid-template-columns: minmax(260px, 320px) minmax(0, 1fr);
  gap: 1rem;
  align-items: start;
}

.panel {
  background: var(--panel);
  border: 1px solid var(--panel-border);
  border-radius: 24px;
  box-shadow: var(--shadow);
  backdrop-filter: blur(16px);
}

/* ── Controls column ──────────────────────────────────────────────────── */

.controls {
  padding: 1rem;
  display: flex;
  flex-direction: column;
  gap: 0.65rem;
}

.control-group > label {
  display: block;
  margin-bottom: 0.35rem;
  font-weight: 700;
  font-size: 0.88rem;
}

.seg-control {
  display: grid;
  background: rgba(21,48,77,0.07);
  border-radius: 14px;
  padding: 3px;
}
.seg-control.cols-2 { grid-template-columns: 1fr 1fr; }

.seg-btn {
  padding: 0.42rem 0.3rem;
  border: 0; border-radius: 11px;
  font: inherit; font-size: 0.82rem; font-weight: 700;
  color: var(--muted); background: transparent;
  cursor: pointer; text-align: center; line-height: 1.2;
  transition: background 0.15s, color 0.15s;
}
.seg-btn.active { background: white; color: var(--ink); box-shadow: 0 2px 8px rgba(21,48,77,0.12); }

/* Fix-it navigation */
.fixit-nav {
  display: flex;
  align-items: center;
  gap: 0.4rem;
}
.nav-btn {
  padding: 0.35rem 0.6rem;
  border: 1.5px solid rgba(21,48,77,0.14);
  border-radius: 8px;
  font: inherit; font-size: 0.82rem; font-weight: 700;
  background: rgba(255,255,255,0.9); color: var(--ink);
  cursor: pointer;
}
.nav-btn:hover { background: white; }
.nav-btn:disabled { opacity: 0.35; cursor: default; }
.nav-counter { flex: 1; text-align: center; font-size: 0.8rem; font-weight: 700; color: var(--muted); }

.decay-name {
  font-size: 0.82rem; font-weight: 700; color: var(--ink);
  background: rgba(255,255,255,0.7);
  border: 1px solid rgba(21,48,77,0.10);
  border-radius: 8px; padding: 0.4rem 0.6rem;
}

/* Zone selector (free-build mode) */
.zone-selector {
  display: flex; gap: 0.4rem;
}
.zone-sel-btn {
  flex: 1; padding: 0.38rem 0.4rem;
  border: 1.5px solid rgba(21,48,77,0.14);
  border-radius: 8px;
  font: inherit; font-size: 0.8rem; font-weight: 700;
  background: rgba(255,255,255,0.7); color: var(--muted);
  cursor: pointer; transition: background 0.15s, color 0.15s, border-color 0.15s;
}
.zone-sel-btn.active {
  background: var(--ink); color: white; border-color: var(--ink);
}

/* Palette */
.palette-tabs {
  display: flex; gap: 3px;
  background: rgba(21,48,77,0.07);
  border-radius: 10px; padding: 3px;
}
.palette-tab {
  flex: 1; padding: 0.32rem 0.2rem;
  border: 0; border-radius: 7px;
  font: inherit; font-size: 0.75rem; font-weight: 700;
  color: var(--muted); background: transparent;
  cursor: pointer; text-align: center;
  transition: background 0.12s, color 0.12s;
}
.palette-tab.active { background: white; color: var(--ink); box-shadow: 0 1px 4px rgba(21,48,77,0.1); }

.palette-grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(46px, 1fr));
  gap: 4px;
}

.palette-btn {
  padding: 0.32rem 0.2rem;
  border: 1.5px solid transparent;
  border-radius: 8px;
  font: inherit; font-size: 0.9rem; font-weight: 700;
  cursor: pointer; text-align: center;
  transition: filter 0.12s, border-color 0.12s;
  line-height: 1.2;
}
.palette-btn:hover { filter: brightness(0.9); }
.palette-btn:active { filter: brightness(0.8); }

/* Particle category colours */
.cat-quark-light  { background: rgba(251,191,36,0.18); color: #92400e; border-color: rgba(251,191,36,0.45); }
.cat-quark-dark   { background: rgba(96,165,250,0.18); color: #1e3a5f; border-color: rgba(96,165,250,0.45); }
.cat-quark-anti   { background: rgba(165,243,252,0.18); color: #164e63; border-color: rgba(165,243,252,0.35); }
.cat-lepton       { background: rgba(56,189,248,0.18); color: #0c4a6e; border-color: rgba(56,189,248,0.4); }
.cat-antilepton   { background: rgba(244,114,182,0.18); color: #831843; border-color: rgba(244,114,182,0.4); }
.cat-neutrino     { background: rgba(186,230,253,0.25); color: #0e7490; border-color: rgba(186,230,253,0.5); }
.cat-antineutrino { background: rgba(253,186,116,0.18); color: #9a3412; border-color: rgba(253,186,116,0.4); }
.cat-boson        { background: rgba(192,132,252,0.18); color: #5b21b6; border-color: rgba(192,132,252,0.4); }
.cat-hadron-b     { background: rgba(209,250,229,0.4);  color: #064e3b; border-color: rgba(52,211,153,0.4); }
.cat-hadron-m     { background: rgba(255,237,213,0.5);  color: #78350f; border-color: rgba(251,191,36,0.35); }

.more-toggle {
  grid-column: 1 / -1;
  padding: 0.28rem;
  border: 1px dashed rgba(21,48,77,0.2);
  border-radius: 7px;
  font: inherit; font-size: 0.75rem; font-weight: 700; color: var(--muted);
  background: transparent; cursor: pointer; text-align: center;
}
.more-toggle:hover { background: rgba(21,48,77,0.04); }

/* ── Main panel (reaction + conservation) ─────────────────────────────── */

.visual-panel { padding: 1rem; display: flex; flex-direction: column; gap: 0.9rem; }

/* Reaction zone */
.reaction-zone {
  display: flex;
  align-items: stretch;
  gap: 0;
  background: rgba(10,22,40,0.04);
  border: 1px solid rgba(21,48,77,0.08);
  border-radius: 16px;
  overflow: hidden;
  min-height: 120px;
}

.particle-zone {
  flex: 1;
  display: flex;
  flex-direction: column;
  padding: 0.7rem;
  gap: 0.45rem;
}
.particle-zone.zone-active-target {
  background: rgba(15,118,110,0.06);
  outline: 2px solid rgba(15,118,110,0.25);
  outline-offset: -2px;
  border-radius: 14px;
}

.zone-header {
  display: flex;
  justify-content: space-between;
  align-items: center;
}
.zone-label {
  font-size: 0.75rem; font-weight: 700; color: var(--muted);
  text-transform: uppercase; letter-spacing: 0.06em;
}
.zone-clear-btn {
  padding: 0.15rem 0.45rem;
  border: 1px solid rgba(21,48,77,0.14);
  border-radius: 6px;
  font: inherit; font-size: 0.72rem; font-weight: 700; color: var(--muted);
  background: rgba(255,255,255,0.8); cursor: pointer;
}
.zone-clear-btn:hover { color: #991b1b; border-color: #fca5a5; background: #fff5f5; }

.particle-chips {
  display: flex;
  flex-wrap: wrap;
  gap: 5px;
  min-height: 38px;
  align-content: flex-start;
}

.chips-placeholder {
  font-size: 0.78rem; color: rgba(21,48,77,0.28); font-style: italic;
  align-self: center; padding: 0.2rem 0;
}

/* Individual chip */
.particle-chip {
  display: inline-flex; align-items: center; gap: 2px;
  padding: 0.28rem 0.4rem 0.28rem 0.45rem;
  border-radius: 999px;
  border: 1.5px solid transparent;
  font: inherit; font-size: 0.95rem; font-weight: 700;
  cursor: default;
  transition: box-shadow 0.15s;
  white-space: nowrap;
}

/* SACE-style sub/super prefix on chips: baryon (top) and charge (bottom),
   stacked to the left of the particle symbol. */
.quantum-prefix {
  display: inline-flex;
  flex-direction: column;
  align-items: flex-end;
  justify-content: center;
  font-size: 0.6em;
  line-height: 1;
  font-weight: 700;
  color: rgba(0, 0, 0, 0.62);
  text-align: right;
  margin-right: 1px;
  min-width: 0.9em;
}
.qn-top, .qn-bottom { display: block; padding: 0; }
.qn-top    { margin-bottom: 1px; }
.chip-symbol { padding: 0 1px; }

/* Plus separator between chips (forms a readable decay equation) */
.chip-plus {
  display: inline-flex;
  align-items: center;
  padding: 0 3px;
  font-size: 1.05rem;
  font-weight: 700;
  color: var(--muted);
  user-select: none;
}
.chip-remove {
  display: inline-flex; align-items: center; justify-content: center;
  width: 16px; height: 16px;
  border: 0; border-radius: 50%;
  font-size: 0.7rem; font-weight: 900; line-height: 1;
  background: rgba(0,0,0,0.12); color: inherit;
  cursor: pointer; padding: 0; flex-shrink: 0;
}
.chip-remove:hover { background: rgba(0,0,0,0.25); }

/* Chip broken (fix-it highlight) */
.chip-broken {
  box-shadow: 0 0 0 2.5px #f59e0b, 0 0 10px rgba(245,158,11,0.4);
  cursor: pointer;
  animation: pulse-amber 1.8s ease-in-out infinite;
}
@keyframes pulse-amber {
  0%, 100% { box-shadow: 0 0 0 2.5px #f59e0b, 0 0 8px rgba(245,158,11,0.3); }
  50%       { box-shadow: 0 0 0 2.5px #d97706, 0 0 16px rgba(245,158,11,0.55); }
}

/* Chip selected-for-swap (in fix-it, after clicking broken chip) */
.chip-selected-swap {
  box-shadow: 0 0 0 2.5px #38bdf8, 0 0 12px rgba(56,189,248,0.45);
  animation: pulse-blue 1.2s ease-in-out infinite;
}
@keyframes pulse-blue {
  0%, 100% { box-shadow: 0 0 0 2.5px #38bdf8, 0 0 8px rgba(56,189,248,0.3); }
  50%       { box-shadow: 0 0 0 2.5px #0ea5e9, 0 0 18px rgba(56,189,248,0.55); }
}

/* Reaction arrow column */
.reaction-divider {
  display: flex; align-items: center; justify-content: center;
  padding: 0 0.6rem;
  font-size: 1.6rem; font-weight: 700; color: var(--muted);
  flex-shrink: 0;
  border-left: 1px solid rgba(21,48,77,0.08);
  border-right: 1px solid rgba(21,48,77,0.08);
}

/* Conservation table */
.conservation-section { display: flex; flex-direction: column; gap: 0.35rem; }
.conservation-title {
  font-size: 0.78rem; font-weight: 700; color: var(--muted);
  text-transform: uppercase; letter-spacing: 0.06em;
}

.verdict-table { display: flex; flex-direction: column; gap: 2px; }

.verdict-row {
  display: grid;
  grid-template-columns: 1fr auto auto auto auto;
  gap: 0.5rem;
  align-items: center;
  padding: 0.38rem 0.7rem;
  border-radius: 8px;
  background: rgba(255,255,255,0.55);
  border: 1px solid rgba(21,48,77,0.07);
  font-size: 0.86rem;
  transition: background 0.2s, border-color 0.2s;
}
.verdict-row.ok   { background: rgba(209,250,229,0.55); border-color: rgba(52,211,153,0.3); }
.verdict-row.fail { background: rgba(254,226,226,0.6);  border-color: rgba(252,165,165,0.4); }
.verdict-row.empty { opacity: 0.45; }

.verdict-label { font-weight: 700; color: var(--ink); }
.verdict-val {
  font-weight: 700; font-variant-numeric: tabular-nums;
  min-width: 3.2ch; text-align: right; color: var(--ink);
}
.verdict-arrow-cell { color: var(--muted); font-size: 0.8rem; }
.verdict-icon { font-size: 1rem; width: 1.2em; text-align: center; }
.verdict-row.ok   .verdict-icon { color: #059669; }
.verdict-row.fail .verdict-icon { color: #dc2626; }

/* Per-particle quantum-number breakdown grid (transposed; columns mirror eqn) */
.verdict-table { overflow-x: auto; }

.qn-empty {
  padding: 0.8rem 0.8rem;
  font-size: 0.85rem;
  font-style: italic;
  color: rgba(21,48,77,0.45);
  text-align: center;
  background: rgba(255,255,255,0.55);
  border-radius: 10px;
}

.qn-table {
  display: grid;
  /* grid-template-columns is set inline per-render based on particle count */
  gap: 1px;
  background: rgba(21,48,77,0.12);
  border: 1px solid rgba(21,48,77,0.12);
  border-radius: 10px;
  overflow: hidden;
  font-size: 0.84rem;
  min-width: max-content;
}
.qn-table > * {
  background: rgba(255,255,255,0.78);
  padding: 0.3rem 0.45rem;
  text-align: center;
  font-variant-numeric: tabular-nums;
  display: flex;
  align-items: center;
  justify-content: center;
}

/* Header row (top): per-particle symbols, operators, total/check labels */
.qn-h {
  background: rgba(21,48,77,0.08);
  font-weight: 700;
  font-size: 0.74rem;
  text-transform: uppercase;
  color: var(--muted);
  letter-spacing: 0.04em;
}
.qn-h.qn-sym {
  font-size: 1.05rem;
  text-transform: none;
  color: var(--ink);
  letter-spacing: 0;
  background: rgba(21,48,77,0.04);
}
.qn-h.qn-op {
  font-size: 1.1rem;
  text-transform: none;
  color: var(--muted);
  background: rgba(21,48,77,0.04);
  padding-left: 0.2rem; padding-right: 0.2rem;
}
.qn-h.qn-arrow { color: var(--ink); font-weight: 700; }
.qn-h.qn-sum-h, .qn-h.qn-check-h { font-size: 0.72rem; }

/* QN label column (leftmost) */
.qn-lbl {
  text-align: left;
  justify-content: flex-start;
  font-weight: 700;
  color: var(--ink);
  cursor: help;
}

/* Operator cells (+ and → between particle columns) — slim, muted */
.qn-op {
  color: var(--muted);
  font-weight: 700;
  padding-left: 0.15rem !important;
  padding-right: 0.15rem !important;
  background: rgba(255,255,255,0.55);
}
.qn-arrow { color: var(--ink); font-size: 0.95rem; }

/* Per-particle value cells */
.qn-cell { color: var(--ink); }

/* Σ columns and OK? column at the right */
.qn-sum {
  background: rgba(15,118,110,0.10);
  font-weight: 700;
  color: #0f766e;
}
.qn-check {
  background: white;
  font-weight: 700;
  font-size: 1.05rem;
}

/* Auto-computed OK? cell (not a student input) */
.qn-check-auto { padding: 0.14rem 0.12rem; }
.qn-ok-cell {
  font-size: 1rem;
  font-weight: 700;
  color: var(--muted);
}
.qn-ok-cell.qn-ok   { color: #059669; }
.qn-ok-cell.qn-fail { color: #dc2626; }
.qn-ok   { color: #059669; }
.qn-fail { color: #dc2626; }

/* Editable cells — text inputs and select for "Conserved?" column */
.qn-cell-input { padding: 0.14rem 0.12rem; }
.qn-input {
  width: 100%;
  min-width: 0;
  padding: 0.18rem 0.1rem;
  border: 1.5px solid rgba(21,48,77,0.18);
  border-radius: 5px;
  font: inherit;
  font-size: 0.82rem;
  font-weight: 700;
  text-align: center;
  background: rgba(255,255,255,0.95);
  color: var(--ink);
  font-variant-numeric: tabular-nums;
}
.qn-input:focus {
  outline: none;
  border-color: var(--accent);
  box-shadow: 0 0 0 2px rgba(15,118,110,0.22);
}

.qn-select {
  width: 100%;
  min-width: 0;
  padding: 0.22rem 0.2rem;
  border: 1.5px solid rgba(21,48,77,0.18);
  border-radius: 6px;
  font: inherit;
  font-size: 0.82rem;
  font-weight: 700;
  background: rgba(255,255,255,0.95);
  color: var(--ink);
  cursor: pointer;
}
.qn-select:focus { outline: none; border-color: var(--accent); box-shadow: 0 0 0 2px rgba(15,118,110,0.22); }

/* Correct / wrong states */
.qn-input.qn-correct, .qn-select.qn-correct {
  background: rgba(209,250,229,0.85);
  border-color: rgba(52,211,153,0.7);
  color: #065f46;
}
.qn-input.qn-wrong, .qn-select.qn-wrong {
  background: rgba(254,226,226,0.85);
  border-color: rgba(252,165,165,0.75);
  color: #991b1b;
}

/* Action bar below the table */
.qn-actions {
  display: flex;
  flex-wrap: wrap;
  align-items: center;
  gap: 0.5rem;
  margin-top: 0.55rem;
}
.qn-btn {
  padding: 0.4rem 0.85rem;
  border: 1.5px solid var(--accent);
  border-radius: 8px;
  font: inherit;
  font-size: 0.84rem;
  font-weight: 700;
  cursor: pointer;
  background: var(--accent);
  color: white;
  transition: filter 0.15s, background 0.15s, color 0.15s;
}
.qn-btn:hover { filter: brightness(1.08); }
.qn-btn:active { filter: brightness(0.95); }
.qn-btn.secondary {
  background: rgba(255,255,255,0.85);
  color: var(--accent);
}
.qn-btn.secondary:hover { background: white; }

.qn-score {
  margin-left: auto;
  font-size: 0.86rem;
  font-weight: 700;
  color: var(--muted);
}
.qn-score.complete { color: #059669; }
.qn-score.partial  { color: #b45309; }

/* Decay note and cross-links */
.decay-note {
  font-size: 0.8rem; color: var(--muted); font-style: italic;
  padding: 0.35rem 0.1rem;
  display: none;
}
.decay-note.visible { display: block; }

.mechanism-link {
  display: inline-flex; align-items: center; gap: 0.3rem;
  font-size: 0.8rem; font-weight: 700; color: var(--accent);
  text-decoration: none;
  padding: 0.3rem 0;
}
.mechanism-link:hover { text-decoration: underline; }
.mechanism-link.hidden { display: none; }

.success-banner {
  display: none;
  padding: 0.6rem 0.9rem;
  background: rgba(209,250,229,0.7);
  border: 1.5px solid rgba(52,211,153,0.5);
  border-radius: 10px;
  font-size: 0.88rem; font-weight: 700; color: #065f46;
  text-align: center;
}
.success-banner.visible { display: block; }

@media (max-width: 900px) {
  .layout { grid-template-columns: 1fr; }
  .hero { flex-direction: column; align-items: flex-start; }
}