/* Kalman / LQR playground, in the Walenberg minimal style: white page, Helvetica, small spaced capitals */

:root {
  --ink: #111;
  --muted: #8a8a8a;
  --line: #e6e6e6;
  --soft: #f4f4f4;
  --accent: #2a6df4;
  --warn: #d2462f;
}

html, body {
  margin: 0;
  background: #fff;
  color: var(--ink);
  font-family: "Helvetica Neue", Helvetica, Arial, sans-serif;
  -webkit-tap-highlight-color: transparent;
}

#wrapper {
  max-width: 1280px;
  margin: 0 auto;
  padding: 0 16px 64px;
}

header {
  padding: 32px 0 20px;
  text-align: center;
}

header h1 {
  margin: 12px 0 6px;
  font-weight: 400;
  font-size: clamp(18px, 4vw, 32px);
  letter-spacing: 0.18em;
  text-transform: uppercase;
}

.sub {
  margin: 0 auto;
  max-width: 640px;
  color: var(--muted);
  font-size: 13px;
  line-height: 1.6;
}

.back-link {
  display: inline-block;
  padding: 12px 8px;
  color: var(--muted);
  text-decoration: none;
  font-size: 11px;
  letter-spacing: 0.12em;
  text-transform: uppercase;
}

.nc { text-transform: none; }

.back-link:hover, .back-link:focus-visible { color: var(--ink); outline: none; }

.label, .section-label, legend, .ctl label, .readout dt {
  color: var(--muted);
  font-size: 11px;
  letter-spacing: 0.12em;
  text-transform: uppercase;
}

.section-label {
  display: flex;
  align-items: center;
  gap: 16px;
  margin: 48px 0 24px;
}

.section-label::after {
  content: "";
  flex: 1;
  height: 1px;
  background: var(--line);
}

/* ---------- playground ---------- */

.play {
  display: grid;
  grid-template-columns: minmax(0, 1fr) 320px;
  gap: 32px;
  align-items: start;
}

.stage-wrap { min-width: 0; }

#stage {
  display: block;
  width: 100%;
  aspect-ratio: 16 / 10;
  background: #fff;
  border: 1px solid var(--line);
  cursor: crosshair;
  touch-action: none;
}

.legend {
  display: flex;
  flex-wrap: wrap;
  gap: 6px 20px;
  margin: 10px 0 0;
  padding: 0;
  list-style: none;
  font-size: 11px;
  letter-spacing: 0.08em;
  text-transform: uppercase;
  color: var(--muted);
}

.legend i {
  display: inline-block;
  width: 10px;
  height: 10px;
  margin-right: 6px;
  vertical-align: -1px;
  border-radius: 50%;
}

.charts {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 20px;
  margin-top: 24px;
}

.chart canvas {
  display: block;
  width: 100%;
  height: 120px;
  border-top: 1px solid var(--line);
}

.chart .label { display: block; margin-bottom: 8px; }

.readout {
  display: grid;
  grid-template-columns: repeat(4, 1fr);
  gap: 12px;
  margin: 24px 0 0;
}

.readout div { border-top: 1px solid var(--line); padding-top: 8px; }
.readout dt { margin-bottom: 4px; }
.readout dd { margin: 0; font-size: 18px; font-variant-numeric: tabular-nums; }
.readout dd small { color: var(--muted); font-size: 11px; }

/* ---------- controls ---------- */

.panel { display: flex; flex-direction: column; gap: 20px; }

fieldset {
  margin: 0;
  padding: 12px 0 0;
  border: 0;
  border-top: 1px solid var(--line);
}

legend { padding: 0 8px 0 0; color: var(--ink); }

.ctl { display: grid; grid-template-columns: 1fr auto; align-items: center; gap: 2px 8px; margin: 10px 0; }
.ctl label { letter-spacing: 0.08em; }
.ctl output { font-size: 12px; font-variant-numeric: tabular-nums; }
.ctl input[type="range"] { grid-column: 1 / -1; width: 100%; margin: 4px 0 0; accent-color: var(--ink); }

.check { display: flex; align-items: center; gap: 8px; margin: 10px 0; font-size: 12px; }
.check input { accent-color: var(--ink); }

.seg { display: flex; flex-wrap: wrap; gap: 6px; margin: 8px 0; }

.seg button, .btns button {
  padding: 7px 10px;
  border: 1px solid var(--line);
  background: #fff;
  color: var(--ink);
  font: inherit;
  font-size: 11px;
  letter-spacing: 0.1em;
  text-transform: uppercase;
  cursor: pointer;
}

.seg button[aria-pressed="true"] { background: var(--ink); border-color: var(--ink); color: #fff; }
.seg button:hover, .btns button:hover { border-color: var(--ink); }
.btns { display: flex; gap: 6px; }
.btns button { flex: 1; }

.hint { margin: 4px 0 0; color: var(--muted); font-size: 12px; line-height: 1.5; }

/* ---------- equations and matrices ---------- */

.eqs {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(min(100%, 460px), 1fr));
  gap: 32px 48px;
}

.eq-card h3, .mat-card h3 {
  margin: 0 0 12px;
  font-weight: 400;
  font-size: 12px;
  letter-spacing: 0.14em;
  text-transform: uppercase;
}

.eq-card p { margin: 10px 0; font-size: 13px; line-height: 1.6; color: #444; }
.tex { overflow-x: auto; overflow-y: hidden; padding: 2px 0; font-size: 14px; }
.katex-display { margin: 0.6em 0; }

.mats {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(min(100%, 380px), 1fr));
  gap: 28px 32px;
}

.mat-card { min-width: 0; }
.mat-card .tex { font-size: 13px; }
.mat-card .note { margin: 6px 0 0; color: var(--muted); font-size: 11px; line-height: 1.5; letter-spacing: 0.04em; }

#zplane { display: block; width: 100%; max-width: 320px; aspect-ratio: 1; }

.stats { font-size: 13px; line-height: 1.8; font-variant-numeric: tabular-nums; }
.stats b { font-weight: 400; color: var(--muted); font-size: 11px; letter-spacing: 0.1em; text-transform: uppercase; margin-right: 6px; }

@media (max-width: 900px) {
  .play { grid-template-columns: 1fr; }
  .readout { grid-template-columns: repeat(2, 1fr); }
}

@media (max-width: 560px) {
  .charts { grid-template-columns: 1fr; }
}