/* ===== RESET ===== */
*, *::before, *::after { box-sizing: border-box; margin: 0; padding: 0; }

:root {
  /* Paper palette */
  --paper:         #f5f0e8;
  --paper-dark:    #ede8df;
  --paper-darker:  #e0d9ce;
  --ink:           #1a1612;
  --ink-mid:       #4a4540;
  --ink-light:     #8a8278;
  --ink-faint:     #c8c0b4;

  /* Accent — deep indigo ink */
  --blue:          #1a3a6b;
  --blue-mid:      #2d5fa8;
  --blue-light:    #4a7fd4;
  --blue-faint:    rgba(26, 58, 107, 0.08);

  /* Curve colors */
  --curve:         #1a3a6b;
  --curve-2:       #8b2020;

  /* Grid */
  --grid-major:    rgba(26, 58, 107, 0.12);
  --grid-minor:    rgba(26, 58, 107, 0.05);
  --axis:          rgba(26, 58, 107, 0.45);

  /* Error */
  --red:           #8b2020;
  --red-faint:     rgba(139, 32, 32, 0.08);

  /* Typography */
  --font-serif:    'Lora', Georgia, serif;
  --font-sans:     'DM Sans', system-ui, sans-serif;
  --font-mono:     'DM Mono', 'Courier New', monospace;

  --radius-sm:     3px;
  --radius:        6px;
  --t:             0.18s ease;
}

/* ===== FONTS ===== */
@import url('https://fonts.googleapis.com/css2?family=Lora:ital,wght@0,400;0,600;1,400&family=DM+Sans:wght@300;400;500&family=DM+Mono:wght@300;400&display=swap');

html, body {
  height: 100%;
  background: var(--paper);
  color: var(--ink);
  font-family: var(--font-sans);
  font-size: 13px;
  overflow: hidden;
}

/* ===== PAPER TEXTURE ===== */
body::before {
  content: '';
  position: fixed;
  inset: 0;
  pointer-events: none;
  z-index: 0;
  opacity: 0.4;
  background-image:
    url("data:image/svg+xml,%3Csvg xmlns='http://www.w3.org/2000/svg' width='300' height='300'%3E%3Cfilter id='n'%3E%3CfeTurbulence type='fractalNoise' baseFrequency='0.75' numOctaves='4' stitchTiles='stitch'/%3E%3CfeColorMatrix type='saturate' values='0'/%3E%3C/filter%3E%3Crect width='300' height='300' filter='url(%23n)' opacity='0.08'/%3E%3C/svg%3E");
}

/* ===== APP ===== */
.app {
  position: relative;
  z-index: 1;
  display: flex;
  flex-direction: column;
  height: 100vh;
  overflow: hidden;
}

/* ===== HEADER ===== */
.header {
  display: flex;
  align-items: baseline;
  justify-content: space-between;
  padding: 14px 28px 13px;
  border-bottom: 2px solid var(--ink);
  background: var(--paper);
  flex-shrink: 0;
}

.header-left { display: flex; align-items: baseline; gap: 16px; }

.title {
  font-family: var(--font-serif);
  font-size: 18px;
  font-weight: 600;
  color: var(--ink);
  letter-spacing: -0.01em;
}

.title-sub {
  font-family: var(--font-serif);
  font-style: italic;
  font-size: 13px;
  color: var(--ink-light);
}

.header-right {
  display: flex;
  align-items: center;
  gap: 20px;
}

.header-tag {
  font-family: var(--font-mono);
  font-size: 10px;
  color: var(--ink-light);
  letter-spacing: 0.06em;
  text-transform: uppercase;
  border: 1px solid var(--ink-faint);
  padding: 2px 8px;
  border-radius: 2px;
}

/* ===== MAIN LAYOUT ===== */
.main {
  display: grid;
  grid-template-columns: 272px 1fr 220px;
  flex: 1;
  overflow: hidden;
}

/* ===== PANELS ===== */
.panel {
  background: var(--paper);
  border-right: 1px solid var(--paper-darker);
  overflow-y: auto;
  overflow-x: hidden;
  padding: 20px 18px;
  display: flex;
  flex-direction: column;
  gap: 22px;
}

.panel-right {
  border-right: none;
  border-left: 1px solid var(--paper-darker);
  background: var(--paper-dark);
}

.panel::-webkit-scrollbar { width: 3px; }
.panel::-webkit-scrollbar-track { background: transparent; }
.panel::-webkit-scrollbar-thumb { background: var(--ink-faint); }

/* ===== SECTION ===== */
.section { display: flex; flex-direction: column; gap: 10px; }

.section-label {
  font-family: var(--font-sans);
  font-size: 9px;
  font-weight: 500;
  letter-spacing: 0.14em;
  text-transform: uppercase;
  color: var(--ink-light);
  padding-bottom: 7px;
  border-bottom: 1px solid var(--paper-darker);
}

/* ===== FUNCTION INPUT ===== */
.input-group {
  display: flex;
  align-items: center;
  gap: 0;
  border: 1px solid var(--ink-faint);
  border-radius: var(--radius-sm);
  background: white;
  overflow: hidden;
  transition: border-color var(--t), box-shadow var(--t);
}

.input-group:focus-within {
  border-color: var(--blue-mid);
  box-shadow: 0 0 0 3px rgba(45, 95, 168, 0.1);
}

.input-prefix {
  font-family: var(--font-serif);
  font-style: italic;
  font-size: 14px;
  color: var(--blue);
  padding: 8px 10px 8px 12px;
  background: var(--paper-dark);
  border-right: 1px solid var(--ink-faint);
  white-space: nowrap;
  flex-shrink: 0;
}

.func-input {
  flex: 1;
  background: transparent;
  border: none;
  outline: none;
  color: var(--ink);
  font-family: var(--font-mono);
  font-size: 13px;
  padding: 8px 12px;
  caret-color: var(--blue);
}

.func-input::placeholder { color: var(--ink-faint); }

.func-error {
  font-size: 11px;
  color: var(--red);
  padding: 6px 10px;
  background: var(--red-faint);
  border: 1px solid rgba(139,32,32,0.2);
  border-radius: var(--radius-sm);
  font-family: var(--font-mono);
}

.func-error.hidden { display: none; }

/* ===== PARAM LIST ===== */
.param-list { display: flex; flex-direction: column; gap: 10px; }

.param-item {
  border: 1px solid var(--paper-darker);
  border-radius: var(--radius);
  padding: 10px 12px;
  background: white;
  transition: border-color var(--t), box-shadow var(--t);
  animation: slideIn 0.2s ease;
}

@keyframes slideIn {
  from { opacity: 0; transform: translateY(-4px); }
  to   { opacity: 1; transform: translateY(0); }
}

.param-item:hover {
  border-color: var(--blue-light);
  box-shadow: 0 1px 6px rgba(26,58,107,0.08);
}

.param-header {
  display: flex;
  align-items: center;
  justify-content: space-between;
  margin-bottom: 9px;
}

.param-name {
  font-family: var(--font-serif);
  font-style: italic;
  font-size: 15px;
  font-weight: 600;
  color: var(--blue);
}

.param-value-display {
  font-family: var(--font-mono);
  font-size: 12px;
  color: var(--ink-mid);
  min-width: 44px;
  text-align: right;
  background: var(--paper-dark);
  padding: 1px 6px;
  border-radius: 2px;
  border: 1px solid var(--ink-faint);
}

.param-slider {
  width: 100%;
  -webkit-appearance: none;
  appearance: none;
  height: 2px;
  background: var(--ink-faint);
  border-radius: 1px;
  outline: none;
  cursor: pointer;
  margin-bottom: 8px;
}

.param-slider::-webkit-slider-thumb {
  -webkit-appearance: none;
  width: 13px; height: 13px;
  border-radius: 50%;
  background: var(--blue);
  border: 2px solid white;
  box-shadow: 0 1px 4px rgba(26,58,107,0.3);
  cursor: pointer;
  transition: transform var(--t);
}

.param-slider::-webkit-slider-thumb:hover {
  transform: scale(1.25);
}

.param-range-row {
  display: flex;
  align-items: center;
  gap: 6px;
  font-size: 10px;
  color: var(--ink-light);
}

.param-range-input {
  width: 50px;
  background: var(--paper-dark);
  border: 1px solid var(--ink-faint);
  border-radius: var(--radius-sm);
  color: var(--ink);
  font-family: var(--font-mono);
  font-size: 10px;
  padding: 2px 5px;
  outline: none;
  text-align: center;
  transition: border-color var(--t);
}

.param-range-input:focus { border-color: var(--blue-mid); }

.param-remove {
  background: none;
  border: none;
  color: var(--ink-faint);
  cursor: pointer;
  font-size: 15px;
  line-height: 1;
  padding: 0 2px;
  transition: color var(--t);
}

.param-remove:hover { color: var(--red); }

.btn-add-param {
  background: transparent;
  border: 1px dashed var(--ink-faint);
  border-radius: var(--radius-sm);
  color: var(--ink-light);
  font-family: var(--font-sans);
  font-size: 11px;
  padding: 7px;
  cursor: pointer;
  transition: all var(--t);
}

.btn-add-param:hover {
  border-color: var(--blue-mid);
  color: var(--blue-mid);
  background: var(--blue-faint);
}

/* ===== RANGE GRID ===== */
.range-grid {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 8px;
}

.range-item { display: flex; flex-direction: column; gap: 4px; }

.range-item label {
  font-size: 10px;
  color: var(--ink-light);
  letter-spacing: 0.04em;
}

.range-input {
  background: white;
  border: 1px solid var(--ink-faint);
  border-radius: var(--radius-sm);
  color: var(--ink);
  font-family: var(--font-mono);
  font-size: 12px;
  padding: 5px 8px;
  outline: none;
  width: 100%;
  transition: border-color var(--t);
}

.range-input:focus { border-color: var(--blue-mid); }

/* ===== PRESETS ===== */
.preset-group-label {
  font-size: 9px;
  font-weight: 500;
  letter-spacing: 0.1em;
  text-transform: uppercase;
  color: var(--blue-mid);
  padding: 6px 0 4px;
  border-bottom: 1px solid rgba(45,95,168,0.15);
  margin-top: 2px;
}

.preset-list {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 5px;
}

.preset-btn {
  background: white;
  border: 1px solid var(--paper-darker);
  border-radius: var(--radius-sm);
  color: var(--ink-mid);
  font-family: var(--font-sans);
  font-size: 11px;
  font-weight: 400;
  padding: 6px 5px;
  cursor: pointer;
  transition: all var(--t);
  text-align: center;
  line-height: 1.3;
}

.preset-btn:hover {
  border-color: var(--blue-mid);
  color: var(--blue);
  background: var(--blue-faint);
}

.preset-btn.active {
  border-color: var(--blue);
  color: var(--blue);
  background: var(--blue-faint);
  font-weight: 500;
}

/* ===== CANVAS ===== */
.canvas-wrapper {
  position: relative;
  display: flex;
  flex-direction: column;
  background: white;
  overflow: hidden;
  border-left: 1px solid var(--paper-darker);
  border-right: 1px solid var(--paper-darker);
}

.canvas-container {
  flex: 1;
  position: relative;
  overflow: hidden;
}

#graphCanvas {
  display: block;
  width: 100%;
  height: 100%;
  cursor: crosshair;
}

.canvas-overlay {
  position: absolute;
  inset: 0;
  pointer-events: none;
}

.coord-display {
  position: absolute;
  bottom: 14px;
  left: 14px;
  background: rgba(245, 240, 232, 0.92);
  border: 1px solid var(--paper-darker);
  border-radius: var(--radius-sm);
  padding: 4px 10px;
  font-family: var(--font-mono);
  font-size: 11px;
  color: var(--ink-mid);
  backdrop-filter: blur(4px);
  opacity: 0;
  transition: opacity 0.2s;
}

.coord-display.visible { opacity: 1; }

.canvas-controls {
  position: absolute;
  top: 14px;
  right: 14px;
  display: flex;
  flex-direction: column;
  gap: 3px;
}

.ctrl-btn {
  width: 28px; height: 28px;
  background: rgba(245, 240, 232, 0.9);
  border: 1px solid var(--paper-darker);
  border-radius: var(--radius-sm);
  color: var(--ink-mid);
  font-size: 14px;
  cursor: pointer;
  display: flex;
  align-items: center;
  justify-content: center;
  transition: all var(--t);
  backdrop-filter: blur(4px);
  font-family: var(--font-sans);
}

.ctrl-btn:hover {
  border-color: var(--blue-mid);
  color: var(--blue);
  background: white;
}

/* ===== RIGHT PANEL ===== */
.info-card {
  background: white;
  border: 1px solid var(--paper-darker);
  border-radius: var(--radius);
  overflow: hidden;
}

.info-row {
  display: flex;
  flex-direction: column;
  gap: 3px;
  padding: 9px 12px;
  border-bottom: 1px solid var(--paper-dark);
}

.info-row:last-child { border-bottom: none; }

.info-key {
  font-size: 9px;
  font-weight: 500;
  letter-spacing: 0.1em;
  text-transform: uppercase;
  color: var(--ink-light);
}

.info-val {
  font-family: var(--font-mono);
  font-size: 11px;
  color: var(--blue);
  word-break: break-all;
}

/* ===== KEY POINTS ===== */
.key-points { display: flex; flex-direction: column; gap: 5px; }

.key-point-item {
  display: flex;
  justify-content: space-between;
  align-items: baseline;
  padding: 6px 10px;
  background: white;
  border: 1px solid var(--paper-darker);
  border-radius: var(--radius-sm);
  font-size: 11px;
  animation: fadeIn 0.25s ease;
}

@keyframes fadeIn {
  from { opacity: 0; }
  to   { opacity: 1; }
}

.key-point-label { color: var(--ink-light); font-size: 10px; }
.key-point-val   { font-family: var(--font-mono); color: var(--blue); font-size: 11px; }

/* ===== PARAM DESC ===== */
.param-desc {
  display: flex;
  flex-direction: column;
  gap: 8px;
  font-size: 11px;
  color: var(--ink-light);
  line-height: 1.65;
}

.param-desc code {
  font-family: var(--font-mono);
  font-size: 10px;
  color: var(--blue-mid);
  background: var(--paper-dark);
  padding: 1px 5px;
  border-radius: 2px;
  border: 1px solid var(--paper-darker);
}

/* ===== EXPORT ===== */
.btn-export {
  width: 100%;
  background: var(--blue);
  border: none;
  border-radius: var(--radius-sm);
  color: white;
  font-family: var(--font-sans);
  font-size: 11px;
  font-weight: 500;
  padding: 9px;
  cursor: pointer;
  letter-spacing: 0.04em;
  transition: background var(--t);
}

.btn-export:hover { background: var(--blue-mid); }

/* ===== SCROLLBAR ===== */
::-webkit-scrollbar { width: 3px; height: 3px; }
::-webkit-scrollbar-track { background: transparent; }
::-webkit-scrollbar-thumb { background: var(--ink-faint); }

/* ===== RESPONSIVE ===== */
@media (max-width: 900px) {
  .main { grid-template-columns: 240px 1fr; }
  .panel-right { display: none; }
}