:root {
  --bg: #0f1216;
  --bg-elev: #161a21;
  --bg-card: #1b2029;
  --border: #2a3140;
  --text: #e6e9ef;
  --text-dim: #9aa3b2;
  --accent: #6ea8ff;
  --accent-2: #9f7aea;
  --ok: #5bd6a1;
  --warn: #ffb55a;
  --proof-bg: #131722;
  --shadow: 0 6px 20px rgba(0,0,0,.35);
  --radius: 12px;
}

html[data-theme="light"] {
  --bg: #f6f7fb;
  --bg-elev: #ffffff;
  --bg-card: #ffffff;
  --border: #e3e6ee;
  --text: #1b1f27;
  --text-dim: #5b6473;
  --accent: #2b6cb0;
  --accent-2: #6b46c1;
  --ok: #2f855a;
  --warn: #b7791f;
  --proof-bg: #f1f3f8;
  --shadow: 0 4px 14px rgba(20,30,50,.08);
}

* { box-sizing: border-box; }

html, body {
  margin: 0;
  padding: 0;
  background: var(--bg);
  color: var(--text);
  font-family: 'Inter', -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, Helvetica, Arial, sans-serif;
  font-size: 15.5px;
  line-height: 1.55;
  -webkit-font-smoothing: antialiased;
}

.topbar {
  position: sticky;
  top: 0;
  z-index: 50;
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 18px;
  padding: 14px 22px;
  background: linear-gradient(180deg, var(--bg-elev), color-mix(in srgb, var(--bg-elev) 92%, transparent));
  border-bottom: 1px solid var(--border);
  backdrop-filter: blur(6px);
}

.brand { display: flex; align-items: center; gap: 14px; }
.brand .logo {
  width: 42px; height: 42px;
  border-radius: 10px;
  display: grid; place-items: center;
  font-size: 22px; font-weight: 700;
  background: linear-gradient(135deg, var(--accent), var(--accent-2));
  color: white;
  box-shadow: var(--shadow);
}
.brand h1 { margin: 0; font-size: 17px; letter-spacing: .2px; }
.brand .sub { margin: 0; font-size: 12.5px; color: var(--text-dim); }

.controls { display: flex; align-items: center; gap: 8px; }
#search {
  width: 380px; max-width: 40vw;
  padding: 9px 12px;
  border-radius: 10px;
  border: 1px solid var(--border);
  background: var(--bg-card);
  color: var(--text);
  outline: none;
  transition: border-color .15s, box-shadow .15s;
}
#search:focus { border-color: var(--accent); box-shadow: 0 0 0 3px color-mix(in srgb, var(--accent) 25%, transparent); }

.controls button {
  width: 36px; height: 36px;
  border-radius: 10px;
  border: 1px solid var(--border);
  background: var(--bg-card);
  color: var(--text);
  cursor: pointer;
  font-size: 16px;
  transition: background .15s, transform .05s;
}
.controls button:hover { background: color-mix(in srgb, var(--accent) 12%, var(--bg-card)); }
.controls button:active { transform: scale(.96); }

.layout {
  display: grid;
  grid-template-columns: 280px 1fr;
  min-height: calc(100vh - 73px);
}

.sidebar {
  border-right: 1px solid var(--border);
  background: var(--bg-elev);
  padding: 18px 14px;
  position: sticky;
  top: 73px;
  align-self: start;
  max-height: calc(100vh - 73px);
  overflow-y: auto;
}

#toc h3 {
  margin: 14px 8px 6px;
  font-size: 11.5px;
  text-transform: uppercase;
  letter-spacing: 1.4px;
  color: var(--text-dim);
}
#toc a {
  display: block;
  padding: 7px 10px;
  border-radius: 8px;
  color: var(--text);
  text-decoration: none;
  font-size: 13.8px;
  border-left: 2px solid transparent;
  transition: background .12s, border-color .12s, color .12s;
}
#toc a:hover { background: color-mix(in srgb, var(--accent) 10%, transparent); }
#toc a.active { background: color-mix(in srgb, var(--accent) 15%, transparent); border-left-color: var(--accent); color: var(--accent); }

main { padding: 26px 36px 80px; max-width: 1100px; }

.chapter {
  margin-bottom: 42px;
  scroll-margin-top: 90px;
}
.chapter-header {
  display: flex; align-items: baseline; gap: 12px;
  margin-bottom: 8px;
}
.chapter h2 {
  margin: 0;
  font-size: 24px;
  letter-spacing: .2px;
  background: linear-gradient(90deg, var(--accent), var(--accent-2));
  -webkit-background-clip: text; background-clip: text; color: transparent;
}
.chapter .chip {
  font-size: 11.5px;
  padding: 3px 8px;
  border-radius: 999px;
  background: color-mix(in srgb, var(--accent) 18%, transparent);
  color: var(--accent);
  border: 1px solid color-mix(in srgb, var(--accent) 30%, transparent);
}
.chapter-intro {
  color: var(--text-dim);
  font-size: 14px;
  margin: 4px 0 18px;
  max-width: 80ch;
}

.card {
  background: var(--bg-card);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 18px 20px;
  margin-bottom: 14px;
  box-shadow: var(--shadow);
  scroll-margin-top: 90px;
}
.card h3 {
  margin: 0 0 8px;
  font-size: 16px;
  display: flex; align-items: center; gap: 10px;
}
.card h3 .num {
  font-size: 12px;
  color: var(--text-dim);
  font-weight: 500;
  font-variant-numeric: tabular-nums;
}
.card h3 .badge {
  margin-left: auto;
  font-size: 10.5px;
  font-weight: 700;
  text-transform: uppercase;
  letter-spacing: 0.8px;
  padding: 2px 8px;
  border-radius: 999px;
}
.card h3 .badge.hors-cours {
  background: color-mix(in srgb, var(--warn) 18%, transparent);
  color: var(--warn);
  border: 1px solid color-mix(in srgb, var(--warn) 35%, transparent);
}
.card.has-badge h3 { display: flex; align-items: center; gap: 10px; }
.card.has-badge {
  border-left: 3px solid color-mix(in srgb, var(--warn) 50%, var(--border));
}
.card .explain {
  color: var(--text-dim);
  font-size: 14px;
  margin: 4px 0 10px;
}
.eq {
  background: var(--proof-bg);
  border: 1px solid var(--border);
  padding: 12px 16px;
  border-radius: 10px;
  overflow-x: auto;
  margin: 8px 0;
}
.eq.center { display: flex; justify-content: center; }

details.proof {
  margin-top: 10px;
  background: var(--proof-bg);
  border: 1px solid var(--border);
  border-radius: 10px;
  padding: 0;
  overflow: hidden;
  transition: border-color .15s;
}
details.proof[open] { border-color: color-mix(in srgb, var(--accent) 40%, var(--border)); }
details.proof summary {
  cursor: pointer;
  padding: 10px 14px;
  font-size: 13.5px;
  font-weight: 600;
  color: var(--accent);
  user-select: none;
  list-style: none;
  display: flex; align-items: center; gap: 8px;
}
details.proof summary::-webkit-details-marker { display: none; }
details.proof summary::before {
  content: "▸";
  display: inline-block;
  transition: transform .15s;
  color: var(--accent);
}
details.proof[open] summary::before { transform: rotate(90deg); }
details.proof .body {
  padding: 4px 16px 16px;
  border-top: 1px solid var(--border);
  font-size: 14px;
  color: var(--text);
}
details.proof .body p { margin: 8px 0; }
details.proof .body ol, details.proof .body ul { padding-left: 22px; }

.tag-row { display: flex; gap: 6px; flex-wrap: wrap; margin-top: 8px; }
.tag {
  font-size: 11px;
  color: var(--text-dim);
  background: color-mix(in srgb, var(--text-dim) 12%, transparent);
  padding: 2px 8px;
  border-radius: 999px;
}

/* ===== Schéma bloc Kalman ===== */
.kf-diagram {
  display: flex;
  flex-direction: column;
  gap: 14px;
  padding: 20px;
  background: var(--proof-bg);
  border-radius: 12px;
  border: 1px solid var(--border);
  margin: 10px 0;
}

.kf-input {
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: 4px;
}
.kf-input .lbl {
  font-size: 11px;
  text-transform: uppercase;
  letter-spacing: 1.2px;
  color: var(--text-dim);
  font-weight: 700;
}
.kf-input .arr {
  font-size: 22px;
  color: var(--accent);
  line-height: 1;
}
.kf-input .var {
  background: color-mix(in srgb, var(--accent) 12%, transparent);
  border: 1px solid color-mix(in srgb, var(--accent) 35%, transparent);
  color: var(--accent);
  padding: 6px 14px;
  border-radius: 999px;
  font-size: 14px;
}

.kf-main {
  display: grid;
  grid-template-columns: minmax(220px, 1fr) auto minmax(220px, 1fr) auto;
  gap: 10px;
  align-items: stretch;
}

.kf-block {
  position: relative;
  border: 2px solid var(--accent);
  border-radius: 12px;
  padding: 14px 16px;
  background: var(--bg-card);
  display: flex;
  flex-direction: column;
  gap: 6px;
}
.kf-block.filt { border-color: var(--accent-2); }
.kf-block h4 {
  margin: 0 0 2px;
  font-size: 14px;
  font-weight: 700;
  letter-spacing: 0.8px;
  color: var(--accent);
}
.kf-block.filt h4 { color: var(--accent-2); }
.kf-block .sub {
  font-size: 11.5px;
  color: var(--text-dim);
  margin: 0 0 6px;
}
.kf-block .eqline {
  font-size: 12.5px;
  padding: 4px 8px;
  border-radius: 6px;
  background: color-mix(in srgb, var(--accent) 6%, transparent);
  border-left: 2px solid color-mix(in srgb, var(--accent) 40%, transparent);
}
.kf-block.filt .eqline {
  background: color-mix(in srgb, var(--accent-2) 6%, transparent);
  border-left-color: color-mix(in srgb, var(--accent-2) 40%, transparent);
}
.kf-block .eqline .num {
  display: inline-block;
  width: 24px;
  font-weight: 700;
  color: var(--accent);
  font-size: 11px;
}
.kf-block.filt .eqline .num { color: var(--accent-2); }

.kf-arrow {
  display: flex;
  flex-direction: column;
  justify-content: center;
  align-items: center;
  text-align: center;
  gap: 6px;
  min-width: 160px;
  padding: 8px 6px;
}
.kf-arrow .lbl {
  font-size: 11px;
  text-transform: uppercase;
  letter-spacing: 1.2px;
  color: var(--accent);
  font-weight: 700;
}
.kf-arrow .shaft {
  width: 100%;
  height: 2px;
  background: var(--accent);
  position: relative;
}
.kf-arrow .shaft::after {
  content: "";
  position: absolute;
  right: -1px; top: 50%;
  width: 0; height: 0;
  border-left: 10px solid var(--accent);
  border-top: 6px solid transparent;
  border-bottom: 6px solid transparent;
  transform: translateY(-50%);
}
.kf-arrow .vars {
  font-size: 12px;
  color: var(--text);
  line-height: 1.5;
}

.kf-outputs {
  display: flex;
  flex-direction: column;
  justify-content: center;
  gap: 8px;
  min-width: 140px;
}
.kf-outputs .out {
  display: flex;
  align-items: center;
  gap: 8px;
  font-size: 13px;
}
.kf-outputs .out .arr {
  color: var(--accent-2);
  font-size: 18px;
}

.kf-feedback {
  display: flex;
  align-items: center;
  justify-content: center;
  gap: 10px;
  padding: 12px 14px;
  border: 1px dashed color-mix(in srgb, var(--accent-2) 60%, transparent);
  border-radius: 12px;
  background: color-mix(in srgb, var(--accent-2) 6%, transparent);
  font-size: 12.5px;
  color: var(--text);
}
.kf-feedback .delay {
  background: var(--accent-2);
  color: white;
  font-weight: 700;
  padding: 4px 10px;
  border-radius: 6px;
  font-size: 12px;
}
.kf-feedback .back-arr {
  color: var(--accent-2);
  font-size: 22px;
  line-height: 1;
}

@media (max-width: 880px) {
  .kf-main { grid-template-columns: 1fr; }
  .kf-arrow .shaft { width: 80%; height: 2px; transform: rotate(90deg); margin: 14px auto; }
}

a.link-card {
  display: block;
  text-decoration: none;
  color: var(--text);
  transition: transform .08s, border-color .15s, box-shadow .15s;
  position: relative;
}
a.link-card:hover {
  border-color: color-mix(in srgb, var(--accent) 55%, var(--border));
  transform: translateY(-1px);
  box-shadow: 0 10px 24px rgba(0,0,0,.32);
}
a.link-card h3 .open-icon {
  margin-left: auto;
  font-size: 14px;
  color: var(--accent);
  opacity: 0.6;
  transition: opacity .15s, transform .15s;
}
a.link-card:hover h3 .open-icon {
  opacity: 1;
  transform: translate(2px, -2px);
}
a.link-card h3 { display: flex; align-items: center; gap: 10px; }

.hidden { display: none !important; }
.hl { background: color-mix(in srgb, var(--warn) 30%, transparent); border-radius: 3px; padding: 0 2px; }

footer {
  border-top: 1px solid var(--border);
  padding: 18px 26px;
  color: var(--text-dim);
  font-size: 13px;
  text-align: center;
}

@media (max-width: 900px) {
  .layout { grid-template-columns: 1fr; }
  .sidebar { position: static; max-height: none; border-right: none; border-bottom: 1px solid var(--border); }
  main { padding: 22px 18px 60px; }
  #search { width: 200px; }
}