/* ==========================================================================
   Ciechanowski-inspired Technical Essay Design System
   ========================================================================== */

:root {
  --bg-paper: #faf8f5;
  --bg-canvas: #f1ede6;
  --bg-panel: #f5f2ec;
  --bg-card: #ffffff;
  --border-subtle: #e2dcd3;
  --border-strong: #cfc7ba;

  --text-main: #232220;
  --text-muted: #66615a;
  --text-faint: #928c83;

  /* 7 Mechanical Color Families */
  --part-red: #d9463e;
  --part-gold: #d99b26;
  --part-blue: #2b72d6;
  --part-green: #2e9e5b;
  --part-purple: #8a4fd6;
  --part-orange: #d96b27;
  --part-silver: #7c8594;

  --font-serif: 'Noto Serif SC', 'Source Han Serif SC', 'Songti SC', 'STSong', Georgia, serif;
  --font-sans: 'Inter', -apple-system, BlinkMacSystemFont, 'PingFang SC', 'Hiragino Sans GB', 'Microsoft YaHei', sans-serif;
  --font-mono: 'JetBrains Mono', 'SF Mono', Menlo, Monaco, Consolas, monospace;

  --content-width: 680px;
  --figure-width: 820px;
}

*, *::before, *::after {
  box-sizing: border-box;
}

html {
  scroll-behavior: smooth;
  font-size: 16px;
  -webkit-font-smoothing: antialiased;
}

body {
  margin: 0;
  padding: 0;
  background-color: var(--bg-paper);
  color: var(--text-main);
  font-family: var(--font-serif);
  line-height: 1.85;
  overflow-x: hidden;
}

/* ==========================================================================
   Top Progress Bar & Sticky Navigation
   ========================================================================== */

.reading-progress {
  position: fixed;
  top: 0;
  left: 0;
  width: 0%;
  height: 3px;
  background: linear-gradient(90deg, var(--part-red), var(--part-gold), var(--part-blue), var(--part-green));
  z-index: 1000;
  transition: width 0.08s linear;
}

.site-nav {
  position: sticky;
  top: 0;
  z-index: 900;
  background: rgba(250, 248, 245, 0.92);
  backdrop-filter: blur(10px);
  -webkit-backdrop-filter: blur(10px);
  border-bottom: 1px solid var(--border-subtle);
  font-family: var(--font-sans);
}

.site-nav-inner {
  max-width: 1040px;
  margin: 0 auto;
  padding: 10px 20px;
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 16px;
}

.nav-brand {
  font-size: 0.875rem;
  font-weight: 700;
  color: var(--text-main);
  letter-spacing: 0.02em;
  white-space: nowrap;
  text-decoration: none;
}

.nav-chapters {
  display: flex;
  align-items: center;
  gap: 6px;
  overflow-x: auto;
  scrollbar-width: none;
  padding-bottom: 2px;
}

.nav-chapters::-webkit-scrollbar {
  display: none;
}

.nav-link {
  font-size: 0.78rem;
  font-weight: 500;
  color: var(--text-muted);
  text-decoration: none;
  padding: 4px 10px;
  border-radius: 999px;
  white-space: nowrap;
  transition: background-color 0.15s, color 0.15s;
}

.nav-link:hover {
  background-color: #ebe6dd;
  color: var(--text-main);
}

.nav-link.active {
  background-color: var(--text-main);
  color: var(--bg-paper);
}

/* ==========================================================================
   Article Header & Typography
   ========================================================================== */

.article-header {
  max-width: var(--content-width);
  margin: 64px auto 40px;
  padding: 0 20px;
}

.article-kicker {
  font-family: var(--font-sans);
  font-size: 0.8rem;
  font-weight: 600;
  letter-spacing: 0.12em;
  text-transform: uppercase;
  color: var(--part-red);
  margin-bottom: 12px;
}

.article-title {
  font-family: var(--font-sans);
  font-size: clamp(2rem, 4.2vw, 2.8rem);
  font-weight: 800;
  line-height: 1.22;
  letter-spacing: -0.02em;
  color: #181715;
  margin: 0 0 18px;
}

.article-subtitle {
  font-size: 1.12rem;
  line-height: 1.75;
  color: var(--text-muted);
  margin: 0 0 24px;
}

.article-meta {
  font-family: var(--font-sans);
  font-size: 0.82rem;
  color: var(--text-faint);
  display: flex;
  flex-wrap: wrap;
  gap: 16px;
  padding-top: 16px;
  border-top: 1px solid var(--border-subtle);
}

.essay-container {
  padding-bottom: 96px;
}

.chapter {
  margin-top: 64px;
  scroll-margin-top: 64px;
}

.prose {
  max-width: var(--content-width);
  margin: 0 auto;
  padding: 0 20px;
}

.prose h2 {
  font-family: var(--font-sans);
  font-size: 1.65rem;
  font-weight: 750;
  line-height: 1.35;
  color: #181715;
  margin: 56px 0 20px;
  padding-bottom: 10px;
  border-bottom: 2px solid var(--border-subtle);
  display: flex;
  align-items: baseline;
  gap: 12px;
}

.chapter-num {
  font-family: var(--font-mono);
  font-size: 0.9rem;
  font-weight: 600;
  color: var(--part-red);
  background: rgba(217, 70, 62, 0.1);
  padding: 2px 8px;
  border-radius: 6px;
}

.prose h3 {
  font-family: var(--font-sans);
  font-size: 1.22rem;
  font-weight: 700;
  color: #1f1e1c;
  margin: 36px 0 14px;
}

.prose p {
  margin: 0 0 1.35em;
  font-size: 1.05rem;
  text-align: justify;
  text-justify: inter-ideograph;
}

.prose ul, .prose ol {
  margin: 0 0 1.4em;
  padding-left: 1.4em;
}

.prose li {
  margin-bottom: 0.55em;
  font-size: 1.03rem;
}

.prose strong {
  font-weight: 700;
  color: #161514;
}

/* Formula & Principle Callout Box */
.formula-box {
  background: #f5f2eb;
  border-left: 3px solid var(--part-blue);
  border-radius: 0 8px 8px 0;
  padding: 14px 18px;
  margin: 22px 0;
  font-family: var(--font-sans);
}

.formula-title {
  font-size: 0.78rem;
  font-weight: 700;
  text-transform: uppercase;
  letter-spacing: 0.06em;
  color: var(--part-blue);
  margin-bottom: 6px;
}

.formula-math {
  font-family: var(--font-mono);
  font-size: 0.98rem;
  font-weight: 600;
  color: #1c1b19;
  margin: 4px 0;
}

.formula-desc {
  font-size: 0.9rem;
  color: var(--text-muted);
  line-height: 1.6;
  margin: 4px 0 0;
}

/* ==========================================================================
   Inline Color-Coded Part Tags (Text <-> 3D Synchronization)
   ========================================================================== */

.part-tag {
  display: inline-flex;
  align-items: center;
  gap: 5px;
  font-family: var(--font-sans);
  font-size: 0.9em;
  font-weight: 600;
  padding: 1px 7px 2px;
  margin: 0 2px;
  border-radius: 5px;
  cursor: pointer;
  transition: transform 0.12s ease, box-shadow 0.15s ease, background-color 0.15s ease;
  vertical-align: baseline;
  border: 1px solid transparent;
  user-select: none;
}

.part-tag::before {
  content: '';
  display: inline-block;
  width: 7px;
  height: 7px;
  border-radius: 50%;
  flex-shrink: 0;
}

.part-tag:hover, .part-tag.is-active {
  transform: translateY(-1px);
  box-shadow: 0 2px 6px rgba(0, 0, 0, 0.09);
}

.part-tag[data-color="red"] {
  color: #9f251e;
  background-color: rgba(217, 70, 62, 0.12);
  border-color: rgba(217, 70, 62, 0.25);
}
.part-tag[data-color="red"]::before { background-color: var(--part-red); }
.part-tag[data-color="red"]:hover, .part-tag[data-color="red"].is-active {
  background-color: rgba(217, 70, 62, 0.22);
  border-color: var(--part-red);
}

.part-tag[data-color="gold"] {
  color: #8f6108;
  background-color: rgba(217, 155, 38, 0.14);
  border-color: rgba(217, 155, 38, 0.3);
}
.part-tag[data-color="gold"]::before { background-color: var(--part-gold); }
.part-tag[data-color="gold"]:hover, .part-tag[data-color="gold"].is-active {
  background-color: rgba(217, 155, 38, 0.26);
  border-color: var(--part-gold);
}

.part-tag[data-color="blue"] {
  color: #194d99;
  background-color: rgba(43, 114, 214, 0.12);
  border-color: rgba(43, 114, 214, 0.25);
}
.part-tag[data-color="blue"]::before { background-color: var(--part-blue); }
.part-tag[data-color="blue"]:hover, .part-tag[data-color="blue"].is-active {
  background-color: rgba(43, 114, 214, 0.22);
  border-color: var(--part-blue);
}

.part-tag[data-color="green"] {
  color: #1a6939;
  background-color: rgba(46, 158, 91, 0.12);
  border-color: rgba(46, 158, 91, 0.25);
}
.part-tag[data-color="green"]::before { background-color: var(--part-green); }
.part-tag[data-color="green"]:hover, .part-tag[data-color="green"].is-active {
  background-color: rgba(46, 158, 91, 0.22);
  border-color: var(--part-green);
}

.part-tag[data-color="purple"] {
  color: #5b2ba0;
  background-color: rgba(138, 79, 214, 0.12);
  border-color: rgba(138, 79, 214, 0.25);
}
.part-tag[data-color="purple"]::before { background-color: var(--part-purple); }
.part-tag[data-color="purple"]:hover, .part-tag[data-color="purple"].is-active {
  background-color: rgba(138, 79, 214, 0.22);
  border-color: var(--part-purple);
}

.part-tag[data-color="orange"] {
  color: #994310;
  background-color: rgba(217, 107, 39, 0.13);
  border-color: rgba(217, 107, 39, 0.28);
}
.part-tag[data-color="orange"]::before { background-color: var(--part-orange); }
.part-tag[data-color="orange"]:hover, .part-tag[data-color="orange"].is-active {
  background-color: rgba(217, 107, 39, 0.24);
  border-color: var(--part-orange);
}

.part-tag[data-color="silver"] {
  color: #464d59;
  background-color: rgba(124, 133, 148, 0.14);
  border-color: rgba(124, 133, 148, 0.28);
}
.part-tag[data-color="silver"]::before { background-color: var(--part-silver); }
.part-tag[data-color="silver"]:hover, .part-tag[data-color="silver"].is-active {
  background-color: rgba(124, 133, 148, 0.25);
  border-color: var(--part-silver);
}

/* ==========================================================================
   3D Interactive Figure Container & Controls
   ========================================================================== */

.interactive-figure {
  max-width: var(--figure-width);
  margin: 34px auto 40px;
  padding: 0 16px;
}

.figure-frame {
  background-color: var(--bg-canvas);
  border: 1px solid var(--border-subtle);
  border-radius: 12px;
  overflow: hidden;
  box-shadow: 0 4px 20px rgba(35, 30, 22, 0.045);
}

.figure-header {
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: 10px 16px;
  background: rgba(255, 255, 255, 0.55);
  border-bottom: 1px solid var(--border-subtle);
  font-family: var(--font-sans);
}

.figure-title {
  font-size: 0.85rem;
  font-weight: 700;
  color: var(--text-main);
  display: flex;
  align-items: center;
  gap: 8px;
}

.figure-badge {
  font-family: var(--font-mono);
  font-size: 0.72rem;
  font-weight: 600;
  color: var(--text-muted);
  background: #e9e3d8;
  padding: 2px 7px;
  border-radius: 4px;
}

.figure-hint-row {
  display: flex;
  align-items: center;
  gap: 10px;
}

.drag-hint {
  font-size: 0.75rem;
  color: var(--text-faint);
  user-select: none;
}

.btn-reset-view,
.btn-toggle-labels {
  font-family: var(--font-sans);
  font-size: 0.75rem;
  font-weight: 600;
  color: var(--text-muted);
  background: var(--bg-card);
  border: 1px solid var(--border-strong);
  border-radius: 5px;
  padding: 3px 9px;
  cursor: pointer;
  transition: background-color 0.12s, color 0.12s, border-color 0.12s;
}

.btn-reset-view:hover,
.btn-toggle-labels:hover {
  background: var(--text-main);
  color: var(--bg-paper);
  border-color: var(--text-main);
}

.btn-toggle-labels.active {
  background: var(--part-blue);
  color: #ffffff;
  border-color: var(--part-blue);
}

.btn-toggle-labels.active:hover {
  background: #235eb3;
  border-color: #235eb3;
}

.canvas-wrapper {
  position: relative;
  width: 100%;
  height: 440px;
  background: radial-gradient(circle at 50% 45%, #f7f4ee 0%, #ede8df 100%);
  cursor: grab;
  touch-action: none;
  user-select: none;
}

.canvas-wrapper.tall {
  height: 500px;
}

.canvas-wrapper:active {
  cursor: grabbing;
}

.canvas-wrapper canvas {
  display: block;
  width: 100%;
  height: 100%;
}

.part-focus-toast {
  position: absolute;
  left: 14px;
  top: 12px;
  background: rgba(24, 23, 21, 0.86);
  color: #faf8f5;
  font-family: var(--font-sans);
  font-size: 0.78rem;
  padding: 5px 11px;
  border-radius: 6px;
  pointer-events: none;
  opacity: 0;
  transform: translateY(-4px);
  transition: opacity 0.18s, transform 0.18s;
  z-index: 10;
}

.part-focus-toast.visible {
  opacity: 1;
  transform: translateY(0);
}

/* ==========================================================================
   Control Panel (Sliders, Segmented Buttons, Telemetry Readouts)
   ========================================================================== */

.controls-panel {
  background: var(--bg-panel);
  border-top: 1px solid var(--border-subtle);
  padding: 14px 18px 16px;
  font-family: var(--font-sans);
  display: flex;
  flex-direction: column;
  gap: 12px;
}

.controls-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(220px, 1fr));
  gap: 12px 20px;
  align-items: center;
}

.control-item {
  display: flex;
  flex-direction: column;
  gap: 6px;
}

.control-label-row {
  display: flex;
  justify-content: space-between;
  align-items: center;
  font-size: 0.82rem;
  font-weight: 600;
  color: var(--text-main);
}

.control-val {
  font-family: var(--font-mono);
  font-size: 0.8rem;
  font-weight: 600;
  color: var(--part-blue);
  background: rgba(43, 114, 214, 0.08);
  padding: 1px 6px;
  border-radius: 4px;
}

/* Custom Range Slider */
input[type="range"].cad-slider {
  -webkit-appearance: none;
  appearance: none;
  width: 100%;
  height: 6px;
  background: #ddd6ca;
  border-radius: 999px;
  outline: none;
  cursor: pointer;
}

input[type="range"].cad-slider::-webkit-slider-thumb {
  -webkit-appearance: none;
  appearance: none;
  width: 18px;
  height: 18px;
  border-radius: 50%;
  background: #ffffff;
  border: 2.5px solid #2b72d6;
  box-shadow: 0 1px 4px rgba(0, 0, 0, 0.22);
  cursor: pointer;
  transition: transform 0.1s ease, border-color 0.15s ease;
}

input[type="range"].cad-slider::-webkit-slider-thumb:hover {
  transform: scale(1.12);
}

input[type="range"].cad-slider.red::-webkit-slider-thumb { border-color: var(--part-red); }
input[type="range"].cad-slider.green::-webkit-slider-thumb { border-color: var(--part-green); }
input[type="range"].cad-slider.orange::-webkit-slider-thumb { border-color: var(--part-orange); }
input[type="range"].cad-slider.purple::-webkit-slider-thumb { border-color: var(--part-purple); }
input[type="range"].cad-slider.gold::-webkit-slider-thumb { border-color: var(--part-gold); }

/* Button Groups & Action Buttons */
.btn-row {
  display: flex;
  flex-wrap: wrap;
  gap: 8px;
  align-items: center;
}

.segmented-group {
  display: inline-flex;
  flex-wrap: wrap;
  background: #e5dfd5;
  padding: 3px;
  border-radius: 8px;
  gap: 3px;
}

.seg-btn {
  font-family: var(--font-sans);
  font-size: 0.78rem;
  font-weight: 600;
  color: var(--text-muted);
  background: transparent;
  border: none;
  padding: 5px 11px;
  border-radius: 6px;
  cursor: pointer;
  transition: background-color 0.14s, color 0.14s, box-shadow 0.14s;
}

.seg-btn:hover {
  color: var(--text-main);
}

.seg-btn.active {
  background: #ffffff;
  color: #181715;
  box-shadow: 0 1px 3px rgba(0, 0, 0, 0.1);
}

.action-btn {
  font-family: var(--font-sans);
  font-size: 0.8rem;
  font-weight: 600;
  color: var(--text-main);
  background: #ffffff;
  border: 1px solid var(--border-strong);
  padding: 6px 13px;
  border-radius: 7px;
  cursor: pointer;
  transition: all 0.14s;
  display: inline-flex;
  align-items: center;
  gap: 6px;
}

.action-btn:hover {
  background: #f0ece4;
  border-color: #a99f90;
}

.action-btn.primary {
  background: var(--part-blue);
  color: #ffffff;
  border-color: var(--part-blue);
}

.action-btn.primary:hover {
  background: #235eb3;
}

.action-btn.danger {
  background: var(--part-red);
  color: #ffffff;
  border-color: var(--part-red);
}

.action-btn.toggle-on {
  background: var(--part-green);
  color: #ffffff;
  border-color: var(--part-green);
}

/* Telemetry Readout Bar */
.telemetry-bar {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(120px, 1fr));
  gap: 8px;
  padding-top: 10px;
  border-top: 1px dashed var(--border-strong);
}

.telemetry-cell {
  background: rgba(255, 255, 255, 0.72);
  border: 1px solid var(--border-subtle);
  border-radius: 7px;
  padding: 6px 10px;
  display: flex;
  flex-direction: column;
  gap: 2px;
}

.telemetry-label {
  font-size: 0.71rem;
  font-weight: 600;
  color: var(--text-muted);
}

.telemetry-value {
  font-family: var(--font-mono);
  font-size: 0.92rem;
  font-weight: 700;
  color: #181715;
}

.telemetry-value.highlight-red { color: var(--part-red); }
.telemetry-value.highlight-blue { color: var(--part-blue); }
.telemetry-value.highlight-green { color: var(--part-green); }
.telemetry-value.highlight-orange { color: var(--part-orange); }
.telemetry-value.highlight-purple { color: var(--part-purple); }

/* Footer */
.article-footer {
  max-width: var(--content-width);
  margin: 72px auto 0;
  padding: 28px 20px 48px;
  border-top: 1px solid var(--border-subtle);
  font-family: var(--font-sans);
  font-size: 0.85rem;
  color: var(--text-muted);
  display: flex;
  justify-content: space-between;
  flex-wrap: wrap;
  gap: 12px;
}

/* ==========================================================================
   Responsive Adjustments
   ========================================================================== */

@media (max-width: 720px) {
  .article-header {
    margin-top: 36px;
  }
  .canvas-wrapper {
    height: 360px;
  }
  .canvas-wrapper.tall {
    height: 410px;
  }
  .drag-hint {
    display: none;
  }
  .controls-grid {
    grid-template-columns: 1fr;
  }
}