/* ─── Reset & Base ──────────────────────────────────────────────────────── */
*, *::before, *::after { box-sizing: border-box; margin: 0; padding: 0; }

:root {
  --bg:          #f0f2f8;
  --surface:     #ffffff;
  --header-bg:   #0f172a;
  --header-text: #f1f5f9;
  --text:        #1e293b;
  --text-muted:  #64748b;
  --accent:      #2563eb;
  --border:      #e2e8f0;
  --radius:      12px;

  /* annotation colours */
  --c-ss:    #dc2626;   /* steady-state — red    */
  --c-tau:   #16a34a;   /* time constant — green */
  --c-peak:  #0891b2;   /* peak overshoot — cyan */
  --c-tr:    #d97706;   /* rise time — amber     */
  --c-ts:    #7c3aed;   /* settling time — violet */
  --c-slope: #64748b;   /* initial slope — slate  */
}

html { font-size: 16px; }

body {
  font-family: system-ui, -apple-system, "Segoe UI", sans-serif;
  background: var(--bg);
  color: var(--text);
  min-height: 100vh;
  line-height: 1.5;
}

/* ─── Header (simulator pages) ───────────────────────────────────────────── */
header {
  background: var(--header-bg);
  color: var(--header-text);
  padding: 1.1rem 2rem;
  user-select: none;
  position: relative;
}

header h1 {
  font-size: 1.35rem;
  font-weight: 700;
  letter-spacing: -0.01em;
}

/* ─── Header (home page) ─────────────────────────────────────────────────── */
.home header {
  padding: 2rem 2rem 1.75rem;
  text-align: center;
}

.home header h1 {
  font-size: 1.75rem;
  letter-spacing: -0.02em;
}

header #fsBtn {
  position: absolute;
  top: 1rem;
  right: 1.5rem;
  background: transparent;
  color: #94a3b8;
  border: 1.5px solid #475569;
  padding: 5px 10px;
  font-size: 0.8rem;
  line-height: 1;
  border-radius: 6px;
  cursor: pointer;
  transition: color 0.15s, border-color 0.15s, background 0.15s;
}
header #fsBtn:hover {
  color: #f1f5f9;
  border-color: #94a3b8;
  background: rgba(255, 255, 255, 0.06);
}

/* ─── Subtitle ───────────────────────────────────────────────────────────── */
.subtitle {
  font-size: 0.82rem;
  color: #94a3b8;
  margin-top: 0.2rem;
  line-height: 2.2;
}

.home .subtitle {
  font-size: 0.9rem;
  font-family: inherit;
  line-height: 1.5;
  letter-spacing: 0.03em;
  text-transform: uppercase;
  margin-top: 0.3rem;
}

/* ─── Back link ──────────────────────────────────────────────────────────── */
.back-link {
  display: inline-block;
  font-size: 0.75rem;
  font-weight: 500;
  color: #94a3b8;
  text-decoration: none;
  margin-bottom: 0.45rem;
  letter-spacing: 0.01em;
  transition: color 0.15s;
}
.back-link:hover { color: #f1f5f9; }

/* ─── Main layout (simulator pages) ─────────────────────────────────────── */
main {
  max-width: 980px;
  margin: 0 auto;
  padding: 1.5rem 1.25rem 3rem;
  display: flex;
  flex-direction: column;
  gap: 1.25rem;
}

/* ─── Main layout (home page) ────────────────────────────────────────────── */
.home main {
  max-width: 860px;
  padding: 2.5rem 1.5rem 4rem;
  display: block;
}

/* ─── Card ───────────────────────────────────────────────────────────────── */
.card {
  background: var(--surface);
  border-radius: var(--radius);
  padding: 1.25rem 1.5rem;
  box-shadow: 0 1px 3px rgba(0,0,0,0.08), 0 1px 8px rgba(0,0,0,0.04);
}

/* ─── Home: simulator grid ───────────────────────────────────────────────── */
.sim-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(320px, 1fr));
  gap: 1.5rem;
}

/* ─── Home: simulator card ───────────────────────────────────────────────── */
.sim-card {
  display: flex;
  flex-direction: column;
  gap: 0.9rem;
  background: var(--surface);
  border-radius: 14px;
  padding: 1.75rem 1.75rem 1.5rem;
  box-shadow: 0 1px 4px rgba(0,0,0,0.07), 0 2px 12px rgba(0,0,0,0.05);
  text-decoration: none;
  color: inherit;
  border: 1.5px solid transparent;
  transition: border-color 0.18s, box-shadow 0.18s, transform 0.18s;
}

.sim-card:hover {
  border-color: var(--accent);
  box-shadow: 0 4px 16px rgba(37, 99, 235, 0.12), 0 1px 4px rgba(0,0,0,0.07);
  transform: translateY(-2px);
}

.sim-badge {
  display: inline-block;
  padding: 0.22rem 0.65rem;
  background: #eff6ff;
  color: var(--accent);
  border: 1px solid #bfdbfe;
  border-radius: 999px;
  font-size: 0.72rem;
  font-weight: 700;
  letter-spacing: 0.04em;
  text-transform: uppercase;
  align-self: flex-start;
}

.sim-card h2 {
  font-size: 1.15rem;
  font-weight: 700;
  color: var(--text);
  letter-spacing: -0.01em;
}

.sim-tf {
  background: #f8fafc;
  border: 1px solid var(--border);
  border-radius: 8px;
  padding: 0.7rem 1rem;
  text-align: center;
  font-size: 1rem;
  color: var(--text);
  min-height: 3rem;
  display: flex;
  align-items: center;
  justify-content: center;
}

.sim-params {
  list-style: none;
  display: flex;
  flex-direction: column;
  gap: 0.3rem;
  font-size: 0.875rem;
  color: var(--text-muted);
  padding-left: 0.1rem;
}

.sim-params li::before {
  content: "·  ";
  color: var(--accent);
  font-weight: 700;
}

.sim-launch {
  margin-top: auto;
  padding-top: 0.5rem;
  font-size: 0.85rem;
  font-weight: 600;
  color: var(--accent);
  letter-spacing: 0.01em;
}

.sim-card:hover .sim-launch { text-decoration: underline; }

/* ─── Controls (1st / 2nd order) ────────────────────────────────────────── */
.controls {
  display: flex;
  flex-wrap: wrap;
  gap: 1.25rem 2.5rem;
  align-items: flex-start;
}

.control-group { flex: 1 1 260px; }

.control-group label {
  display: block;
  font-size: 0.88rem;
  font-weight: 600;
  color: var(--text);
  margin-bottom: 0.55rem;
  line-height: 1.8;
}

.control-group label .param {
  font-size: 1rem;
  font-style: italic;
}

.control-group label .unit {
  font-weight: 400;
  color: var(--text-muted);
  font-size: 0.82rem;
}

.slider-row {
  display: flex;
  align-items: center;
  gap: 0.5rem;
}

.slider-row input[type="range"] {
  flex: 1;
  accent-color: var(--accent);
  height: 5px;
  cursor: pointer;
}

.slider-row input[type="number"] {
  width: 70px;
  padding: 0.3rem 0.45rem;
  border: 1.5px solid var(--border);
  border-radius: 7px;
  font-size: 0.92rem;
  text-align: center;
  color: var(--text);
  background: #f8fafc;
  transition: border-color 0.15s;
}

.slider-row input[type="number"]:focus {
  outline: none;
  border-color: var(--accent);
  background: white;
}

.range-label {
  font-size: 0.74rem;
  color: var(--text-muted);
  min-width: 22px;
  text-align: center;
}

/* ─── System-type badge (2nd-order) ─────────────────────────────────────── */
.badge-row {
  flex: 1 1 100%;
  display: flex;
  justify-content: flex-end;
  align-items: center;
  padding-top: 0.25rem;
}

.badge {
  display: inline-block;
  padding: 0.3rem 0.85rem;
  border-radius: 999px;
  font-size: 0.8rem;
  font-weight: 600;
  letter-spacing: 0.01em;
}

.badge-undamped { background: #fff1f2; color: #9f1239; border: 1.5px solid #fecdd3; }
.badge-under    { background: #ecfeff; color: #0e7490; border: 1.5px solid #a5f3fc; }
.badge-critical { background: #fefce8; color: #854d0e; border: 1.5px solid #fde68a; }
.badge-over     { background: #f0fdf4; color: #166534; border: 1.5px solid #bbf7d0; }

/* ─── PID: control panel ─────────────────────────────────────────────────── */
.panel {
  display: flex;
  flex-wrap: nowrap;
  gap: 10px;
  margin-bottom: 1rem;
  align-items: flex-start;
}

.panel > .group,
.panel-col { flex: 1; }

.panel-col {
  display: flex;
  flex-direction: column;
}

.group {
  display: flex;
  flex-direction: column;
  gap: 6px;
  background: #f8fafc;
  border: 1.5px solid var(--border);
  border-radius: 8px;
  padding: 8px 14px 10px;
}

.group-title {
  font-size: 0.78rem;
  font-weight: 700;
  color: var(--text-muted);
  text-transform: uppercase;
  letter-spacing: 0.04em;
  margin-bottom: 4px;
  padding-bottom: 4px;
  border-bottom: 1px solid var(--border);
}

.group label {
  display: flex;
  align-items: center;
  gap: 7px;
  font-size: 0.875rem;
  white-space: nowrap;
  transition: opacity 0.2s;
}
.group label.disabled { opacity: 0.35; }

.group input[type="range"] {
  width: 120px;
  accent-color: var(--accent);
  cursor: pointer;
}

.group input[type="checkbox"] {
  accent-color: var(--accent);
  cursor: pointer;
  width: 14px;
  height: 14px;
}

.group select {
  padding: 3px 6px;
  font-size: 0.875rem;
  font-family: inherit;
  border-radius: 6px;
  border: 1.5px solid var(--border);
  background: var(--surface);
  color: var(--text);
  cursor: pointer;
}

.val {
  display: inline-block;
  min-width: 48px;
  font-family: "Courier New", Courier, monospace;
  font-weight: 700;
  color: var(--accent);
}

.param-name { font-style: normal; }
.param-name sub { font-style: italic; }

.ref-params {
  display: flex;
  flex-direction: column;
  gap: 6px;
  margin-top: 2px;
  padding-top: 6px;
  border-top: 1px dashed var(--border);
}

/* ─── PID: button row ────────────────────────────────────────────────────── */
.btn-row {
  display: flex;
  flex-wrap: wrap;
  align-items: center;
  gap: 8px;
}

.tw-control {
  display: flex;
  align-items: center;
  gap: 6px;
  margin-left: auto;
  font-size: 0.875rem;
  white-space: nowrap;
}

.tw-control input[type="range"] {
  width: 120px;
  accent-color: var(--accent);
  cursor: pointer;
}

.tw-label {
  color: var(--text-muted);
  font-size: 0.82rem;
}

button {
  padding: 6px 22px;
  font-size: 0.875rem;
  font-family: inherit;
  font-weight: 600;
  border: none;
  border-radius: 7px;
  background: var(--accent);
  color: #fff;
  cursor: pointer;
  transition: background 0.18s;
}
button:hover           { background: #1d4ed8; }
button.secondary       { background: #7c3aed; }
button.secondary:hover { background: #6d28d9; }
button.pause           { background: #ea580c; }
button.pause:hover     { background: #c2410c; }
button.icon-btn {
  background: transparent;
  color: var(--accent);
  border: 1.5px solid var(--accent);
  padding: 5px 10px;
  font-size: 1rem;
  line-height: 1;
}
button.icon-btn:hover { background: #eff6ff; }

/* ─── Chart ──────────────────────────────────────────────────────────────── */
.chart-section { padding: 1rem 1rem 0.75rem; }

.chart-wrap {
  position: relative;
  height: 430px;
}

#plot {
  display: block;
  margin: 0 auto;
  background: #1a1a2e;
  border-radius: 8px;
  max-width: 100%;
  height: auto;
}

/* ─── Characteristics table ──────────────────────────────────────────────── */
.card h2 {
  font-size: 0.95rem;
  font-weight: 600;
  color: var(--text);
  margin-bottom: 0.85rem;
}

.formula-block {
  display: flex;
  flex-wrap: wrap;
  justify-content: center;
  align-items: center;
  gap: 0 3rem;
  margin-bottom: 1.25rem;
  padding: 0.6rem 1rem;
  background: #f8fafc;
  border-radius: 8px;
  border: 1px solid var(--border);
}

.formula-item {
  font-size: 1rem;
  color: var(--text);
}

.table-wrap { overflow-x: auto; }

table {
  width: 100%;
  border-collapse: collapse;
  font-size: 0.875rem;
}

thead th {
  text-align: left;
  padding: 0.45rem 0.85rem;
  background: #f1f5f9;
  font-weight: 600;
  font-size: 0.82rem;
  text-transform: uppercase;
  letter-spacing: 0.04em;
  color: var(--text-muted);
  border-bottom: 2px solid var(--border);
}

tbody td {
  padding: 0.5rem 0.85rem;
  border-bottom: 1px solid #f1f5f9;
  vertical-align: middle;
}

tbody tr:last-child td { border-bottom: none; }
tbody tr:hover td { background: #fafbff; }

td.formula {
  font-size: 0.9rem;
  color: var(--text-muted);
  white-space: nowrap;
}

td.value {
  font-family: "Courier New", Courier, monospace;
  font-weight: 700;
  color: var(--accent);
  white-space: nowrap;
}

.note {
  font-size: 0.78rem;
  color: var(--text-muted);
  font-style: italic;
}

/* annotation colour swatches */
.swatch {
  display: inline-block;
  width: 14px;
  height: 3px;
  border-radius: 2px;
  vertical-align: middle;
  margin-right: 4px;
  position: relative;
  top: -1px;
}
.swatch.ss    { background: var(--c-ss);    }
.swatch.tau   { background: var(--c-tau);   }
.swatch.peak  { background: var(--c-peak);  }
.swatch.tr    { background: var(--c-tr);    }
.swatch.ts    { background: var(--c-ts);    }
.swatch.slope { background: var(--c-slope); }

/* ─── Author footer ──────────────────────────────────────────────────────── */
.author-footer {
  text-align: center;
  font-size: 0.8rem;
  color: var(--text-muted);
  padding-bottom: 0.5rem;
}

.home .author-footer { margin-top: 1.25rem; }
.author-footer a {
  display: inline-flex;
  align-items: center;
  gap: 4px;
  color: var(--text-muted);
  text-decoration: none;
  margin: 0 8px;
  transition: color 0.15s;
}
.author-footer a:hover { color: var(--accent); }

.author-footer .fa-brands {
  font-size: 1.1rem;
  line-height: 1;
  position: relative;
  top: 2px;
}

/* ─── Fullscreen ─────────────────────────────────────────────────────────── */
:fullscreen body,
:-webkit-full-screen body {
  overflow-y: auto;
}

/* ─── Responsive ─────────────────────────────────────────────────────────── */
@media (max-width: 600px) {
  header { padding: 0.9rem 1rem; }
  header h1 { font-size: 1.1rem; }
  main { padding: 1rem 0.75rem 2rem; gap: 1rem; }
  .card { padding: 1rem; }
  .chart-wrap { height: 300px; }
  .group input[type="range"] { width: 90px; }
  .panel { flex-wrap: wrap; }
  thead th:nth-child(4), tbody td:nth-child(4) { display: none; }
  thead th:nth-child(2), tbody td:nth-child(2) { display: none; }
  td.formula { display: none; }
  .badge-row { justify-content: flex-start; }
}

@media (max-width: 540px) {
  .home header { padding: 1.5rem 1rem 1.25rem; }
  .home header h1 { font-size: 1.4rem; }
  .home main { padding: 1.5rem 1rem 3rem; }
  .sim-grid { grid-template-columns: 1fr; }
}