/* Linear Algebra Explorer — styles */
:root {
  --bg: #0b0e14; --panel: #10141c; --elev: #161b25; --border: #232a38; --border-2: #2f3848;
  --text: #e6e9ef; --muted: #8b94a7; --accent: #58c4dd; --accent-dim: rgba(88,196,221,0.14);
  --i: #83c167; --j: #fc6255; --k: #58c4dd; --vec: #f5d547; --warn: #ff8a5b; --good: #83c167; --nul: #d678ff; --colsp: #4ecdc4;
  --font: ui-sans-serif, system-ui, -apple-system, "Segoe UI", Helvetica, Arial, sans-serif;
  --mono: ui-monospace, "SF Mono", Menlo, Consolas, monospace;
  --math: "STIX Two Math", "Latin Modern Math", "Cambria Math", Georgia, "Times New Roman", serif;
  color-scheme: dark;
}
* { box-sizing: border-box; }
html, body { height: 100%; margin: 0; }
body { background: var(--bg); color: var(--text); font-family: var(--font); font-size: 14px; line-height: 1.45;
  display: grid; grid-template-columns: 236px minmax(0, 1fr) 420px; grid-template-rows: 54px minmax(0, 1fr); height: 100%; overflow: hidden; }
a { color: var(--accent); }
button, input, select { font-family: inherit; font-size: inherit; }

/* top bar */
.topbar { grid-column: 1 / -1; display: flex; align-items: center; gap: 14px; padding: 0 14px; border-bottom: 1px solid var(--border); background: var(--panel); min-width: 0; }
.brand { color: var(--text); text-decoration: none; font-weight: 600; white-space: nowrap; letter-spacing: 0.01em; }
.brand-mark { color: var(--accent); font-family: var(--mono); margin-right: 4px; }
.ch-head { display: flex; align-items: baseline; gap: 10px; min-width: 0; flex: 1; border-left: 1px solid var(--border); padding-left: 14px; }
.ch-num { color: var(--muted); font-family: var(--mono); font-size: 12px; white-space: nowrap; }
.ch-head h1 { font-size: 16px; margin: 0; font-weight: 600; white-space: nowrap; }
.ch-summary { color: var(--muted); font-size: 13px; white-space: nowrap; overflow: hidden; text-overflow: ellipsis; }
.nav-btns { display: flex; gap: 6px; }
.icon-btn { display: none; background: none; border: 1px solid var(--border); color: var(--text); border-radius: 6px; width: 32px; height: 32px; cursor: pointer; }

/* sidebar */
.sidebar { overflow: auto; border-right: 1px solid var(--border); background: var(--panel); padding: 10px 0 30px; }
.nav-group h4 { margin: 12px 16px 4px; font-size: 11px; text-transform: uppercase; letter-spacing: 0.1em; color: var(--muted); font-weight: 600; }
.nav-item { display: flex; gap: 10px; align-items: baseline; padding: 7px 16px; color: var(--text); text-decoration: none; font-size: 13.5px; border-left: 2px solid transparent; }
.nav-item:hover { background: var(--elev); }
.nav-item.active { background: var(--accent-dim); border-left-color: var(--accent); }
.nav-num { font-family: var(--mono); font-size: 11px; color: var(--muted); }

/* stage */
.stage-wrap { display: flex; flex-direction: column; min-width: 0; min-height: 0; }
#stage { flex: 1; display: flex; gap: 6px; padding: 6px; min-height: 0; }
.view { position: relative; flex: 1; min-width: 0; min-height: 0; border: 1px solid var(--border); border-radius: 10px; overflow: hidden; background: var(--bg); }
.view canvas { position: absolute; inset: 0; width: 100%; height: 100%; display: block; }
.view-title { position: absolute; top: 8px; left: 10px; max-width: calc(100% - 20px); white-space: nowrap; overflow: hidden; text-overflow: ellipsis; font-size: 12px; color: var(--muted); pointer-events: none; background: rgba(11,14,20,0.6); padding: 2px 6px; border-radius: 4px; }
.view-title b { color: var(--text); font-weight: 600; }
#hint { font-size: 11.5px; color: var(--muted); text-align: center; padding: 0 12px 6px; min-height: 18px; }
.stage-col { display: flex; flex-direction: column; gap: 6px; flex: 1; min-width: 0; }

/* panel */
.panel { overflow: auto; border-left: 1px solid var(--border); background: var(--panel); padding: 12px 14px 60px; }
.group { margin-bottom: 12px; padding: 10px 12px 12px; background: var(--elev); border: 1px solid var(--border); border-radius: 10px; }
.group h3 { margin: 0 0 8px; font-size: 11px; text-transform: uppercase; letter-spacing: 0.1em; color: var(--muted); font-weight: 600; }
.row { display: flex; flex-wrap: wrap; gap: 6px 8px; align-items: center; margin: 6px 0; }
.row.top { align-items: flex-start; }
.btn { background: var(--bg); color: var(--text); border: 1px solid var(--border-2); border-radius: 6px; padding: 5px 10px; cursor: pointer; font-size: 13px; }
.btn:hover { border-color: var(--accent); }
.btn.primary { background: var(--accent-dim); border-color: var(--accent); color: #bfeaf5; }
.btn.small { padding: 3px 8px; font-size: 12px; }
.btn:disabled { opacity: 0.4; cursor: default; }
.btn.active { background: var(--accent-dim); border-color: var(--accent); }
.note { color: var(--muted); font-size: 12.5px; margin: 6px 0 0; }
.err { color: var(--warn); }

/* sliders & inputs */
.slider { display: block; margin: 6px 0; }
.sl-head { display: flex; justify-content: space-between; font-size: 12.5px; color: var(--muted); }
.sl-val { font-family: var(--mono); color: var(--text); }
.slider input[type=range] { width: 100%; accent-color: var(--accent); margin: 2px 0 0; }
.select { display: inline-flex; flex-direction: column; gap: 2px; font-size: 12.5px; color: var(--muted); }
.select select { background: var(--bg); color: var(--text); border: 1px solid var(--border-2); border-radius: 6px; padding: 4px 6px; max-width: 100%; }
.toggle { display: inline-flex; gap: 6px; align-items: center; font-size: 13px; cursor: pointer; margin-right: 8px; }
.toggle input { accent-color: var(--accent); }
.stepper { display: inline-flex; align-items: center; gap: 8px; font-size: 12.5px; color: var(--muted); }
.st-ctl { display: inline-flex; align-items: center; gap: 4px; }
.st-val { font-family: var(--mono); color: var(--text); min-width: 16px; text-align: center; }
.sl-label { font-size: 12.5px; color: var(--muted); }

/* matrices */
.mat-editor { display: inline-block; vertical-align: middle; margin: 4px 8px 4px 0; }
.me-label { font-size: 12.5px; color: var(--muted); margin-bottom: 2px; }
.me-body { display: inline-flex; align-items: stretch; }
.br { display: inline-block; width: 7px; border: 2px solid var(--muted); border-radius: 3px; flex: none; }
.br.l { border-right: none; } .br.r { border-left: none; }
.mg { display: inline-grid; gap: 2px 4px; padding: 3px 4px; align-items: center; justify-items: center; }
.mcell { width: 60px; background: transparent; border: 1px solid transparent; border-radius: 4px; color: var(--text); font-family: var(--mono); font-size: 13.5px; padding: 3px 2px; text-align: center; }
.mat-editor.small .mcell { width: 44px; font-size: 12px; padding: 1px 1px; }
.mcell:hover { border-color: var(--border-2); }
.mcell:focus { outline: none; border-color: var(--accent); background: rgba(88,196,221,0.08); }
.mcell.bad { border-color: var(--warn); }
.mat { display: inline-flex; align-items: stretch; vertical-align: middle; margin: 2px 3px; }
.mat .mg { gap: 1px 10px; padding: 2px 6px; }
.mat .mc { font-family: var(--mono); font-size: 13px; text-align: center; white-space: nowrap; }
.mat.small .mc { font-size: 11.5px; } .mat.small .mg { gap: 0 6px; }
.mat .mc.hl { background: var(--accent-dim); border-radius: 3px; padding: 0 3px; }
.mwrap { display: inline-flex; align-items: center; gap: 6px; margin: 4px 6px 4px 0; }
.mlabel { color: var(--muted); font-size: 13px; }
.mat-display { display: flex; flex-wrap: wrap; align-items: center; gap: 4px 8px; margin: 6px 0; font-size: 14px; }
.formula { text-align: center; padding: 8px 10px; margin: 8px 0; background: var(--bg); border-radius: 8px; font-family: var(--math); font-size: 15px; line-height: 1.7; overflow-x: auto; }
.m { font-family: var(--math); font-style: italic; font-size: 1.05em; }
.m .mat, .formula .mat { font-style: normal; }
b.i { color: var(--i); } b.j { color: var(--j); } b.k { color: var(--k); } b.v { color: var(--vec); } b.n { color: var(--nul); } b.c { color: var(--colsp); } b.a { color: var(--accent); } b.w { color: var(--warn); } b.g { color: var(--good); } b.e1 { color: #ff9f43; } b.e2 { color: #c39bd3; } b.e3 { color: #4ecdc4; } b.p { color: #f08fc0; }
.op { font-family: var(--math); }

/* readouts */
.readout { border-collapse: collapse; width: 100%; font-size: 13px; }
.readout td { padding: 3px 4px; vertical-align: top; border-bottom: 1px solid var(--border); }
.readout tr:last-child td { border-bottom: none; }
.readout .rk { color: var(--muted); white-space: nowrap; width: 38%; }
.readout .rv { font-family: var(--mono); font-size: 12.5px; }
.readout .rv .mat { vertical-align: middle; }
.readout tr.hl td { background: var(--accent-dim); }

/* prose */
.prose { font-size: 13.5px; color: #cfd5e0; }
.prose h2 { font-size: 17px; margin: 10px 0 6px; color: var(--text); }
.prose h4 { font-size: 11px; text-transform: uppercase; letter-spacing: 0.1em; color: var(--accent); margin: 16px 0 6px; }
.prose p { margin: 0 0 9px; }
.prose ul, .prose ol { margin: 0 0 9px; padding-left: 20px; }
.prose li { margin-bottom: 4px; }
.prose code { font-family: var(--mono); font-size: 12px; background: var(--bg); padding: 1px 5px; border-radius: 4px; }
.prose .try { background: var(--elev); border-left: 3px solid var(--vec); padding: 8px 10px; border-radius: 0 8px 8px 0; margin: 10px 0; }
.prose .try h4 { margin: 0 0 6px; color: var(--vec); }
.prose .def { background: var(--elev); border-left: 3px solid var(--accent); padding: 8px 10px; border-radius: 0 8px 8px 0; margin: 10px 0; }
.prose .def h4 { margin: 0 0 4px; }
.prose .mat { vertical-align: middle; }
.cards { display: grid; grid-template-columns: repeat(auto-fill, minmax(150px, 1fr)); gap: 8px; margin: 8px 0; }
.card { display: block; text-decoration: none; color: var(--text); background: var(--elev); border: 1px solid var(--border); border-radius: 8px; padding: 8px 10px; font-size: 12.5px; }
.card:hover { border-color: var(--accent); }
.card b { display: block; color: var(--accent); font-size: 12px; margin-bottom: 2px; }
.kbd { font-family: var(--mono); font-size: 11px; background: var(--bg); border: 1px solid var(--border-2); border-radius: 4px; padding: 0 5px; }
.legend { display: flex; flex-wrap: wrap; gap: 4px 12px; font-size: 12px; color: var(--muted); margin: 4px 0; }
.legend i { display: inline-block; width: 10px; height: 10px; border-radius: 2px; margin-right: 4px; vertical-align: -1px; }
.chips { display: flex; flex-wrap: wrap; gap: 5px; }
.chip { background: var(--bg); border: 1px solid var(--border-2); border-radius: 999px; padding: 3px 10px; font-size: 12px; cursor: pointer; color: var(--text); }
.chip:hover, .chip.active { border-color: var(--accent); color: #bfeaf5; }

/* responsive */
@media (max-width: 1180px) { body { grid-template-columns: 200px minmax(0, 1fr) 360px; } .ch-summary { display: none; } }
@media (max-width: 900px) {
  body { grid-template-columns: 1fr; grid-template-rows: 54px minmax(420px, 60vh) auto; height: auto; overflow: auto; }
  .icon-btn { display: inline-block; }
  .sidebar { position: fixed; top: 54px; left: 0; bottom: 0; width: 260px; z-index: 20; transform: translateX(-100%); transition: transform 0.2s; }
  body.nav-open .sidebar { transform: none; }
  .panel { border-left: none; border-top: 1px solid var(--border); }
  .ch-head { display: none; }
  #stage { flex-direction: column; }
}
@media (max-width: 560px) { .mcell { width: 48px; } body { grid-template-rows: 54px minmax(360px, 55vh) auto; } }