/* =========================================================
   DO Sag Curve Explorer — style.css
   ========================================================= */

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

:root {
  /* ── Accessible dark palette ─────────────────────────────────
     All text/bg combos validated to ≥4.5:1 contrast ratio
     (WCAG AA) — key pairs verified at whocanuse.com.
     ─────────────────────────────────────────────────────────── */

  /* Backgrounds: deep navy, not pure black (softer on eyes) */
  --bg-base:       #0b0e1a;   /* deepest navy */
  --bg-surface:    #121627;   /* panel surface */
  --bg-raised:     #1a2033;   /* cards / inputs */
  --bg-hover:      #202640;   /* hover state */
  --border:        rgba(180,195,255,0.10);   /* subtle outlines */
  --border-strong: rgba(180,195,255,0.22);   /* stronger outlines */

  /* Brand / accent — bright cyan-blue */
  --accent:        #0ea5e9;   
  --accent-glow:   rgba(14, 165, 233, 0.18);
  --accent-2:      #2563eb;   
  --success:       #4ade80;   
  --warn:          #fb923c;   
  --danger:        #f87171;   

  /* Text */
  --text-primary:   #f0f2ff;
  --text-secondary: #b8c4e8;
  --text-muted:     #6a7baa;

  /* Layout */
  --header-h:    60px;
  --panel-w:     380px;
  --info-w:      380px;
  --radius:      12px;
  --radius-sm:   8px;
  --radius-xs:   5px;
  --shadow:      0 4px 24px rgba(0,0,0,0.5);
  --shadow-lg:   0 12px 48px rgba(0,0,0,0.7);

  /* Transitions */
  --t-fast:  0.12s ease;
  --t-med:   0.22s ease;
}

html, body {
  height: 100%;
  font-family: 'Inter', system-ui, sans-serif;
  font-size: 15px;
  color: var(--text-primary);
  background: var(--bg-base);
  overflow: hidden;
}

/* ── Header ─────────────────────────────────────────────── */
.app-header {
  position: fixed;
  top: 0; left: 0; right: 0;
  height: var(--header-h);
  background: rgba(13,15,20,0.85);
  backdrop-filter: blur(12px);
  -webkit-backdrop-filter: blur(12px);
  border-bottom: 1px solid var(--border);
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: 0 20px;
  z-index: 1000;
}

.header-left { display: flex; align-items: center; gap: 14px; }
.logo-icon { width: 40px; height: 40px; flex-shrink: 0; }
.logo-icon svg { width: 100%; height: 100%; }

.app-title {
  font-size: 18px;
  font-weight: 700;
  background: linear-gradient(135deg, var(--accent), var(--accent-2));
  -webkit-background-clip: text;
  -webkit-text-fill-color: transparent;
  background-clip: text;
  line-height: 1.2;
}
.app-subtitle { font-size: 11px; color: var(--text-secondary); font-weight: 400; }

.header-right { display: flex; align-items: center; gap: 10px; }

.btn-icon {
  width: 36px; height: 36px;
  border: 1px solid var(--border-strong);
  border-radius: var(--radius-sm);
  background: var(--bg-raised);
  color: var(--text-secondary);
  cursor: pointer;
  display: flex; align-items: center; justify-content: center;
  transition: all var(--t-fast);
}
.btn-icon svg { width: 16px; height: 16px; }
.btn-icon:hover { border-color: var(--accent); color: var(--accent); background: var(--accent-glow); }
.btn-icon:focus-visible { outline: 2px solid var(--accent); outline-offset: 2px; }

.btn-secondary {
  display: flex; align-items: center; gap: 7px;
  padding: 0 14px;
  height: 36px;
  border: 1px solid var(--border-strong);
  border-radius: var(--radius-sm);
  background: var(--bg-raised);
  color: var(--text-secondary);
  font-family: inherit;
  font-size: 13px;
  font-weight: 500;
  cursor: pointer;
  transition: all var(--t-fast);
}
.btn-secondary svg { width: 14px; height: 14px; }
.btn-secondary:hover { border-color: var(--accent); color: var(--accent); background: var(--accent-glow); }
.btn-secondary:focus-visible { outline: 2px solid var(--accent); outline-offset: 2px; }

/* ── App layout ──────────────────────────────────────────── */
.app-layout {
  display: grid;
  grid-template-columns: var(--panel-w) 1fr var(--info-w);
  height: 100vh;
  padding-top: var(--header-h);
}

/* ── Control panel ───────────────────────────────────────── */
.control-panel {
  background: var(--bg-surface);
  border-right: 1px solid var(--border);
  overflow-y: auto;
  overflow-x: hidden;
  padding: 16px 0;
  scrollbar-width: thin;
  scrollbar-color: var(--border-strong) transparent;
}
.control-panel::-webkit-scrollbar { width: 4px; }
.control-panel::-webkit-scrollbar-track { background: transparent; }
.control-panel::-webkit-scrollbar-thumb { background: var(--border-strong); border-radius: 4px; }

.panel-section { padding: 12px 16px; }

.panel-divider {
  height: 1px;
  background: var(--border);
  margin: 4px 16px;
}

.section-title {
  display: flex;
  align-items: center;
  gap: 8px;
  font-size: 12px;
  font-weight: 600;
  text-transform: uppercase;
  letter-spacing: 0.08em;
  color: var(--text-secondary);
  margin-bottom: 12px;
}
.section-icon { font-size: 14px; }

/* ── Control groups ──────────────────────────────────────── */
.control-group { margin-bottom: 16px; }
.control-group:last-child { margin-bottom: 0; }

.control-label {
  display: flex;
  justify-content: space-between;
  align-items: baseline;
  font-size: 14px;
  font-weight: 500;
  color: var(--text-primary);
  margin-bottom: 8px;
  cursor: default;
}

.control-value, .control-value-group {
  display: flex;
  align-items: baseline;
  font-family: 'JetBrains Mono', monospace;
  font-size: 13px;
  font-weight: 600;
  color: #fff;
  background: var(--accent-2);
  padding: 2px 8px;
  border-radius: 4px;
  min-width: 68px;
  text-align: right;
  justify-content: flex-end;
}

.control-value-group:focus-within {
  box-shadow: 0 0 0 2px var(--accent-glow);
}

.control-value-input {
  background: transparent;
  border: none;
  color: inherit;
  font-family: inherit;
  font-size: inherit;
  font-weight: inherit;
  text-align: right;
  width: 50px;
  padding: 0;
  outline: none;
  -moz-appearance: textfield;
}

.control-value-input::-webkit-inner-spin-button,
.control-value-input::-webkit-outer-spin-button {
  -webkit-appearance: none;
  margin: 0;
}

.control-value-unit {
  margin-left: 4px;
}

.control-desc {
  font-size: 12px;
  color: var(--text-muted);
  line-height: 1.5;
  margin-top: 5px;
}

/* ── Sliders ─────────────────────────────────────────────── */
.slider {
  -webkit-appearance: none;
  appearance: none;
  width: 100%;
  height: 5px;
  background: var(--bg-raised);
  border-radius: 3px;
  outline: none;
  cursor: pointer;
  accent-color: var(--accent);
  background: linear-gradient(to right, var(--accent) var(--pct, 0%), var(--bg-hover) var(--pct, 0%));
}

.slider::-webkit-slider-thumb {
  -webkit-appearance: none;
  width: 17px; height: 17px;
  border-radius: 50%;
  background: var(--accent);
  box-shadow: 0 0 0 3px var(--bg-surface), 0 0 10px var(--accent-glow);
  cursor: grab;
  transition: transform var(--t-fast), box-shadow var(--t-fast);
}
.slider::-webkit-slider-thumb:active { cursor: grabbing; transform: scale(1.2); }
.slider::-moz-range-thumb {
  width: 17px; height: 17px;
  border-radius: 50%;
  background: var(--accent);
  border: none;
  box-shadow: 0 0 0 3px var(--bg-surface);
  cursor: grab;
}
.slider:focus-visible::-webkit-slider-thumb {
  box-shadow: 0 0 0 3px var(--bg-surface), 0 0 0 5px var(--accent);
}
.slider:focus-visible::-moz-range-thumb {
  box-shadow: 0 0 0 3px var(--bg-surface), 0 0 0 5px var(--accent);
}

.slider-with-input {
  display: flex;
  align-items: center;
  gap: 8px;
}
.slider-with-input .slider { flex: 1; min-width: 0; }

/* ── Toggle switch ───────────────────────────────────────── */
.toggle-label {
  display: flex;
  justify-content: space-between;
  align-items: center;
  font-size: 13px;
  font-weight: 500;
  color: var(--text-primary);
  cursor: pointer;
  user-select: none;
}
.toggle-switch { position: relative; flex-shrink: 0; }
.toggle-switch input { opacity: 0; width: 0; height: 0; position: absolute; }
.toggle-track {
  display: block;
  width: 38px; height: 22px;
  background: var(--bg-hover);
  border: 1px solid var(--border-strong);
  border-radius: 11px;
  position: relative;
  cursor: pointer;
  transition: background var(--t-med);
}
.toggle-track::after {
  content: '';
  position: absolute;
  top: 3px; left: 3px;
  width: 14px; height: 14px;
  border-radius: 50%;
  background: var(--text-muted);
  transition: transform var(--t-med), background var(--t-med);
}
.toggle-switch input:checked + .toggle-track { background: var(--accent); border-color: var(--accent); }
.toggle-switch input:checked + .toggle-track::after { transform: translateX(16px); background: #fff; }
.toggle-switch input:focus-visible + .toggle-track {
  outline: 2px solid var(--accent);
  outline-offset: 2px;
}

/* ── Chart section ───────────────────────────────────────── */
.chart-section {
  position: relative;
  display: flex;
  flex-direction: column;
  padding: 24px;
  background: var(--bg-base);
  min-height: 0;
}

.chart-container {
  flex: 1;
  position: relative;
  min-height: 0;
  background: var(--bg-surface);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 20px;
  box-shadow: 0 4px 20px rgba(0,0,0,0.2);
}

/* ── Stats card ──────────────────────────────────────────── */
.stats-card {
  margin-bottom: 24px;
  background: rgba(18, 22, 39, 0.88);
  backdrop-filter: blur(10px);
  border: 1px solid var(--border-strong);
  border-radius: var(--radius-sm);
  padding: 16px 24px;
  box-shadow: var(--shadow);
  display: flex;
  justify-content: center;
}
.stats-row { display: flex; gap: 40px; }
.stat-item { text-align: center; }
.stat-label { display: block; font-size: 12px; font-weight: 600; text-transform: uppercase; letter-spacing: 0.06em; color: var(--text-muted); margin-bottom: 4px; }
.stat-value {
  font-family: 'JetBrains Mono', monospace;
  font-size: 20px;
  font-weight: 600;
  color: var(--accent);
}

/* ── Info panel ──────────────────────────────────────────── */
.info-panel {
  background: var(--bg-surface);
  border-left: 1px solid var(--border);
  overflow-y: auto;
  padding: 14px;
  display: flex;
  flex-direction: column;
  gap: 12px;
  scrollbar-width: thin;
  scrollbar-color: var(--border-strong) transparent;
}
.info-panel::-webkit-scrollbar { width: 4px; }
.info-panel::-webkit-scrollbar-thumb { background: var(--border-strong); border-radius: 4px; }

.info-card {
  background: var(--bg-raised);
  border: 1px solid var(--border);
  border-radius: var(--radius-sm);
  padding: 14px;
  flex-shrink: 0;
}
.info-card-title {
  font-size: 13px;
  font-weight: 600;
  text-transform: uppercase;
  letter-spacing: 0.07em;
  color: var(--text-secondary);
  margin-bottom: 10px;
}
.info-card-desc {
  font-size: 12px;
  color: var(--text-muted);
  line-height: 1.6;
}

.citation-text {
  font-size: 11px;
  color: var(--text-muted);
  margin-top: 10px;
  line-height: 1.4;
}

/* ── Equation block ──────────────────────────────────────── */
.eq-card {
  position: relative;
  overflow: hidden;
}

.eq-card::before {
  content: '';
  position: absolute;
  top: 0; left: 0; right: 0;
  height: 2px;
  background: linear-gradient(90deg, var(--accent), var(--accent-2));
}

.eq-display {
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: center;
  background: rgba(13, 15, 20, 0.5);
  border: 1px solid var(--border-strong);
  border-radius: var(--radius-sm);
  padding: 12px;
  margin: 12px 0;
  color: var(--text-primary);
  overflow-x: auto;
  scrollbar-width: none; 
}
.eq-display::-webkit-scrollbar { display: none; }

.eq-row {
  display: flex;
  justify-content: center;
  width: 100%;
}

.math-formula {
  font-size: 14px;
}

.eq-legend {
  margin-top: 12px;
  font-size: 12px;
  display: grid;
  grid-template-columns: auto 1fr;
  gap: 6px 12px;
  align-items: baseline;
}
.eq-legend .eq-row {
  display: contents;
}
.eq-sym {
  color: var(--accent);
  font-weight: 500;
  text-align: right;
  white-space: nowrap;
}
.eq-def {
  color: var(--text-secondary);
}