:root {
  --bg: #0f1117;
  --surface: #1a1d27;
  --surface2: #232733;
  --border: #2e3345;
  --text: #e2e4ed;
  --text-dim: #8b8fa7;
  --accent: #6c8aff;
  --accent-glow: rgba(108, 138, 255, 0.18);
  --sem1: #5b9aff;
  --sem2: #45d4a8;
  --sem3: #f0a050;
  --sem4: #e06088;
  --vw-math: #a78bfa;
  --vw-phys: #22d3ee;
  --vor-gymi: #f9a8d4;
  --gymi: #86efac;
  --radius: 12px;
  --transition: 0.3s cubic-bezier(0.4, 0, 0.2, 1);
}

* {
  margin: 0;
  padding: 0;
  box-sizing: border-box;
}

body {
  font-family:
    "Segoe UI",
    system-ui,
    -apple-system,
    sans-serif;
  background: var(--bg);
  color: var(--text);
  height: 100vh;
  overflow: hidden;
  display: flex;
  flex-direction: column;
}

/* ── NAV BAR ── */
.hub-back-btn {
  display: inline-flex;
  align-items: center;
  background: var(--surface2);
  border: 1px solid var(--border);
  color: var(--text-dim);
  padding: 5px 12px;
  border-radius: 7px;
  font-size: 0.82rem;
  font-weight: 600;
  text-decoration: none;
  white-space: nowrap;
  transition: var(--transition);
}

.hub-back-btn:hover {
  border-color: var(--accent);
  color: var(--accent);
}

.navbar {
  position: relative;
  flex-shrink: 0;
  z-index: 100;
  background: rgba(15, 17, 23, 0.92);
  backdrop-filter: blur(16px);
  border-bottom: 1px solid var(--border);
  padding: 12px 24px;
  display: flex;
  align-items: center;
  gap: 24px;
  flex-wrap: wrap;
}

.navbar h1 {
  font-size: 1.15rem;
  font-weight: 700;
  white-space: nowrap;
  background: linear-gradient(135deg, var(--sem1), var(--sem3));
  -webkit-background-clip: text;
  -webkit-text-fill-color: transparent;
}

.nav-group {
  display: flex;
  align-items: center;
  gap: 8px;
}

.nav-label {
  font-size: 0.78rem;
  color: var(--text-dim);
  text-transform: uppercase;
  letter-spacing: 0.08em;
}

/* Semester Tabs */
.sem-tabs {
  display: flex;
  gap: 4px;
}

.sem-tab {
  padding: 6px 16px;
  border-radius: 8px;
  border: 1px solid var(--border);
  background: transparent;
  color: var(--text-dim);
  cursor: pointer;
  font-size: 0.82rem;
  font-weight: 600;
  transition: var(--transition);
}

.sem-tab:hover {
  background: var(--surface2);
  color: var(--text);
}

.sem-tab.active {
  border-color: var(--accent);
  color: var(--accent);
  background: var(--accent-glow);
}

.sem-tab[data-sem="all"].active {
  border-color: var(--accent);
}

.sem-tab[data-sem="1"].active {
  border-color: var(--sem1);
  color: var(--sem1);
  background: rgba(91, 154, 255, 0.12);
}

.sem-tab[data-sem="2"].active {
  border-color: var(--sem2);
  color: var(--sem2);
  background: rgba(69, 212, 168, 0.12);
}

.sem-tab[data-sem="3"].active {
  border-color: var(--sem3);
  color: var(--sem3);
  background: rgba(240, 160, 80, 0.12);
}

.sem-tab[data-sem="4"].active {
  border-color: var(--sem4);
  color: var(--sem4);
  background: rgba(224, 96, 136, 0.12);
}

.sem-tab[data-sem="vor-gymi"].active {
  border-color: var(--vor-gymi);
  color: var(--vor-gymi);
  background: rgba(249, 168, 212, 0.12);
}

.sem-tab[data-sem="gymi"].active {
  border-color: var(--gymi);
  color: var(--gymi);
  background: rgba(134, 239, 172, 0.12);
}

/* Abstraction Level Buttons */
.level-btns {
  display: flex;
  gap: 4px;
}

.level-btn {
  padding: 6px 14px;
  border-radius: 8px;
  border: 1px solid var(--border);
  background: transparent;
  color: var(--text-dim);
  cursor: pointer;
  font-size: 0.82rem;
  font-weight: 600;
  transition: var(--transition);
}

.level-btn:hover {
  background: var(--surface2);
  color: var(--text);
}

.level-btn.active {
  border-color: var(--accent);
  color: var(--accent);
  background: var(--accent-glow);
}

/* ── VIEWPORT / CANVAS (pan-zoom) ── */
#viewport {
  flex: 1;
  overflow: hidden;
  position: relative;
  cursor: grab;
  user-select: none;
  -webkit-user-select: none;
}

#viewport.grabbing {
  cursor: grabbing;
}

#canvas {
  position: absolute;
  top: 0;
  left: 0;
  transform-origin: 0 0;
  will-change: transform;
}

/* Zoom controls */
.zoom-controls {
  display: flex;
  align-items: center;
  gap: 4px;
  margin-left: auto;
}

.zoom-btn {
  width: 28px;
  height: 28px;
  border-radius: 6px;
  border: 1px solid var(--border);
  background: transparent;
  color: var(--text-dim);
  cursor: pointer;
  font-size: 1.1rem;
  font-weight: 700;
  line-height: 1;
  display: flex;
  align-items: center;
  justify-content: center;
  transition: var(--transition);
}

.zoom-btn:hover {
  background: var(--surface2);
  color: var(--text);
  border-color: var(--accent);
}

.zoom-btn.wide {
  width: auto;
  padding: 0 10px;
  font-size: 0.75rem;
}

.zoom-level {
  font-size: 0.78rem;
  color: var(--text-dim);
  min-width: 42px;
  text-align: center;
  font-variant-numeric: tabular-nums;
}

/* Map hint */
#map-hint {
  position: absolute;
  bottom: 18px;
  right: 18px;
  background: rgba(26, 29, 39, 0.88);
  border: 1px solid var(--border);
  border-radius: 8px;
  padding: 7px 14px;
  font-size: 0.74rem;
  color: var(--text-dim);
  pointer-events: none;
  opacity: 1;
  transition: opacity 1.2s;
  z-index: 50;
}

/* ── MAIN CONTENT ── */
.container {
  max-width: 1400px;
  margin: 0 auto;
  padding: 28px 24px 60px;
  position: relative;
}

/* Semester Section */
.semester-section {
  margin-bottom: 36px;
}

.semester-section.hidden {
  display: none;
}

.semester-header {
  font-size: 1.3rem;
  font-weight: 700;
  margin-bottom: 16px;
  padding-left: 14px;
  border-left: 4px solid var(--sem1);
}

.semester-section[data-sem="2"] .semester-header {
  border-color: var(--sem2);
}

.semester-section[data-sem="3"] .semester-header {
  border-color: var(--sem3);
}

.semester-section[data-sem="4"] .semester-header {
  border-color: var(--sem4);
}

.semester-section[data-sem="vg-math"] .semester-header {
  border-color: var(--vor-gymi);
}

.semester-section[data-sem="gy-math"] .semester-header {
  border-color: var(--vw-math);
}

.semester-section[data-sem="gy-phys"] .semester-header {
  border-color: var(--vw-phys);
}

/* Section Divider */
.section-divider {
  text-align: center;
  margin: 48px 0 32px;
  position: relative;
}

.section-divider::before {
  content: "";
  position: absolute;
  left: 0;
  right: 0;
  top: 50%;
  height: 1px;
  background: var(--border);
}

.section-divider span {
  position: relative;
  background: var(--bg);
  padding: 0 20px;
  font-size: 0.85rem;
  color: var(--text-dim);
  text-transform: uppercase;
  letter-spacing: 0.1em;
  font-weight: 700;
}

.section-divider.hidden {
  display: none;
}

/* Module Grid */
.module-grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(300px, 1fr));
  gap: 16px;
}

/* Module Card */
.module-card {
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  overflow: hidden;
  cursor: pointer;
  transition: var(--transition);
  position: relative;
}

.module-card::before {
  content: "";
  position: absolute;
  top: 0;
  left: 0;
  right: 0;
  height: 3px;
  background: var(--sem1);
  transition: var(--transition);
}

.semester-section[data-sem="2"] .module-card::before {
  background: var(--sem2);
}

.semester-section[data-sem="3"] .module-card::before {
  background: var(--sem3);
}

.semester-section[data-sem="4"] .module-card::before {
  background: var(--sem4);
}

.semester-section[data-sem="vg-math"] .module-card::before {
  background: var(--vor-gymi);
}

.semester-section[data-sem="gy-math"] .module-card::before {
  background: var(--vw-math);
}

.semester-section[data-sem="gy-phys"] .module-card::before {
  background: var(--vw-phys);
}

.module-card:hover {
  border-color: #444;
  transform: translateY(-2px);
  box-shadow: 0 8px 24px rgba(0, 0, 0, 0.3);
}

.module-card.expanded {
  grid-column: 1 / -1;
  max-width: 900px;
}

.module-header {
  padding: 16px 18px;
  display: flex;
  align-items: center;
  justify-content: space-between;
}

.module-name {
  font-size: 1.05rem;
  font-weight: 700;
}

.module-toggle {
  width: 28px;
  height: 28px;
  border-radius: 50%;
  background: var(--surface2);
  border: 1px solid var(--border);
  color: var(--text-dim);
  display: flex;
  align-items: center;
  justify-content: center;
  font-size: 0.8rem;
  transition: var(--transition);
}

.module-card.expanded .module-toggle,
.module-card.level-open .module-toggle {
  transform: rotate(180deg);
  color: var(--accent);
}

/* Level 2 */
.level2-container {
  max-height: 0;
  overflow: hidden;
  transition:
    max-height 0.4s cubic-bezier(0.4, 0, 0.2, 1),
    padding 0.3s;
  padding: 0 18px;
}

.module-card.expanded .level2-container,
.module-card.level-open .level2-container {
  max-height: 2000px;
  padding: 0 18px 16px;
}

.level2-item {
  margin-bottom: 10px;
  background: var(--surface2);
  border-radius: 8px;
  border: 1px solid transparent;
  transition: var(--transition);
  overflow: hidden;
}

.level2-item:hover {
  border-color: var(--border);
}

.level2-header {
  padding: 10px 14px;
  display: flex;
  align-items: center;
  justify-content: space-between;
  cursor: pointer;
  font-weight: 600;
  font-size: 0.92rem;
}

.level2-toggle {
  font-size: 0.7rem;
  color: var(--text-dim);
  transition: var(--transition);
}

.level2-item.open .level2-toggle {
  transform: rotate(180deg);
  color: var(--accent);
}

/* Level 3 */
.level3-container {
  max-height: 0;
  overflow: hidden;
  transition: max-height 0.35s cubic-bezier(0.4, 0, 0.2, 1);
}

.level2-item.open .level3-container,
.level2-item.level-open .level3-container {
  max-height: 1000px;
}

.level3-list {
  padding: 0 14px 10px 28px;
  display: flex;
  flex-wrap: wrap;
  gap: 6px;
}

.level3-tag {
  padding: 4px 10px;
  background: rgba(108, 138, 255, 0.08);
  border: 1px solid rgba(108, 138, 255, 0.15);
  border-radius: 6px;
  font-size: 0.8rem;
  color: var(--text-dim);
  transition: var(--transition);
}

.level3-tag:hover {
  background: rgba(108, 138, 255, 0.15);
  color: var(--text);
}

/* Level 4 (sub-sub items) */
.level4-group {
  margin-top: 6px;
  padding-left: 8px;
}

.level4-label {
  font-size: 0.78rem;
  color: var(--accent);
  font-weight: 600;
  margin-bottom: 4px;
}

.level4-tags {
  display: flex;
  flex-wrap: wrap;
  gap: 5px;
}

.level4-tag {
  padding: 3px 8px;
  background: rgba(108, 138, 255, 0.05);
  border: 1px solid rgba(108, 138, 255, 0.1);
  border-radius: 5px;
  font-size: 0.75rem;
  color: var(--text-dim);
}

/* Breadcrumb / Zoom indicator */
.zoom-indicator {
  position: fixed;
  bottom: 24px;
  left: 50%;
  transform: translateX(-50%);
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: 10px;
  padding: 8px 20px;
  font-size: 0.82rem;
  color: var(--text-dim);
  display: none;
  align-items: center;
  gap: 10px;
  box-shadow: 0 8px 32px rgba(0, 0, 0, 0.4);
  z-index: 50;
}

.zoom-indicator.visible {
  display: flex;
}

.zoom-indicator button {
  background: var(--accent);
  color: #fff;
  border: none;
  padding: 4px 12px;
  border-radius: 6px;
  cursor: pointer;
  font-size: 0.8rem;
  font-weight: 600;
}

/* ── FOCUS MODE ── */
.focus-btn {
  width: 26px;
  height: 26px;
  border-radius: 50%;
  background: transparent;
  border: 1px solid var(--border);
  cursor: pointer;
  font-size: 0.78rem;
  display: flex;
  align-items: center;
  justify-content: center;
  transition: var(--transition);
  padding: 0;
  line-height: 1;
  flex-shrink: 0;
}

.focus-btn:hover {
  background: rgba(255, 80, 80, 0.15);
  border-color: rgba(255, 80, 80, 0.5);
}

.focus-btn.active {
  background: rgba(255, 80, 80, 0.22);
  border-color: rgba(255, 80, 80, 0.7);
  box-shadow: 0 0 8px rgba(255, 80, 80, 0.35);
}

.module-card.focus-dimmed {
  opacity: 0.13;
  filter: grayscale(0.65);
  pointer-events: none;
  transform: none !important;
  box-shadow: none !important;
}

.module-card.focus-highlight {
  border-color: rgba(255, 80, 80, 0.75) !important;
  box-shadow:
    0 0 0 2px rgba(255, 80, 80, 0.3),
    0 8px 32px rgba(255, 80, 80, 0.2) !important;
}

.module-card.focus-prereq {
  border-color: rgba(255, 210, 60, 0.55) !important;
  box-shadow: 0 0 0 1px rgba(255, 210, 60, 0.2) !important;
}

.focus-indicator {
  position: fixed;
  bottom: 24px;
  left: 50%;
  transform: translateX(-50%);
  background: var(--surface);
  border: 1px solid rgba(255, 80, 80, 0.4);
  border-radius: 10px;
  padding: 8px 20px;
  font-size: 0.82rem;
  color: var(--text-dim);
  display: none;
  align-items: center;
  gap: 12px;
  box-shadow: 0 8px 32px rgba(0, 0, 0, 0.4);
  z-index: 51;
  white-space: nowrap;
}

.focus-indicator.visible {
  display: flex;
}

.focus-indicator #focusPath {
  color: var(--text);
  font-weight: 600;
}

.focus-indicator button {
  background: rgba(255, 80, 80, 0.18);
  color: rgba(255, 130, 130, 1);
  border: 1px solid rgba(255, 80, 80, 0.4);
  padding: 4px 12px;
  border-radius: 6px;
  cursor: pointer;
  font-size: 0.8rem;
  font-weight: 600;
  transition: var(--transition);
}

.focus-indicator button:hover {
  background: rgba(255, 80, 80, 0.32);
}

/* Responsive */
@media (max-width: 768px) {
  .navbar {
    padding: 10px 12px;
    gap: 12px;
  }

  .container {
    padding: 16px 12px 40px;
  }

  .module-grid {
    grid-template-columns: 1fr;
  }

  .module-card.expanded {
    grid-column: 1;
  }
}

/* ── ARROW OVERLAY ── */
#arrow-svg {
  position: absolute;
  top: 0;
  left: 0;
  pointer-events: none;
  z-index: 10;
  overflow: visible;
}

.arrow-toggle {
  padding: 6px 14px;
  border-radius: 8px;
  border: 1px solid var(--border);
  background: transparent;
  color: var(--text-dim);
  cursor: pointer;
  font-size: 0.82rem;
  font-weight: 600;
  transition: var(--transition);
}

.arrow-toggle:hover {
  background: var(--surface2);
  color: var(--text);
}

.arrow-toggle.active {
  border-color: var(--accent);
  color: var(--accent);
  background: var(--accent-glow);
}

/* Responsive tweaks for viewport layout */
@media (max-width: 600px) {
  .zoom-level {
    display: none;
  }
}