/* Robotics Learning Portal — dark techy theme */
:root {
  --bg: #0f1117;
  --surface: #1a1d27;
  --surface-hover: #222633;
  --border: #2a2e3d;
  --accent: #00d4aa;
  --accent-dim: #00d4aa33;
  --accent-glow: #00d4aa55;
  --text: #e0e4ef;
  --text-dim: #8a90a5;
  --progress-bg: #2a2e3d;
  --danger: #ff6b6b;
  --warning: #ffc857;
  --video: #7c5cff;
  --code: #5cb8ff;
  --chat-width: 33.33vw;
}

* { 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);
  line-height: 1.6;
  min-height: 100vh;
}

/* ============ Login Gate ============ */
#login-gate {
  position: fixed;
  inset: 0;
  z-index: 9999;
  background: var(--bg);
  display: flex;
  align-items: center;
  justify-content: center;
}

#login-gate.hidden { display: none; }

.login-box {
  text-align: center;
  max-width: 360px;
  width: 90%;
}

.login-box h1 {
  font-size: 2.2rem;
  font-weight: 700;
  letter-spacing: -0.5px;
  margin-bottom: 0.3rem;
}

.login-box h1 span {
  color: var(--accent);
}

.login-subtitle {
  color: var(--text-dim);
  font-size: 0.95rem;
  margin-bottom: 1.5rem;
}

#login-form {
  display: flex;
  gap: 0.5rem;
}

#login-form.hidden { display: none; }
.login-subtitle.hidden { display: none; }

#login-email {
  flex: 1;
  padding: 0.7rem 1rem;
  border-radius: 8px;
  border: 1px solid var(--border);
  background: var(--surface);
  color: var(--text);
  font-size: 1rem;
  font-family: inherit;
  outline: none;
  transition: border-color 0.2s;
}

#login-email:focus {
  border-color: var(--accent);
}

#login-form button {
  padding: 0.7rem 1.3rem;
  border-radius: 8px;
  border: none;
  background: var(--accent);
  color: var(--bg);
  font-size: 0.95rem;
  font-weight: 600;
  font-family: inherit;
  cursor: pointer;
  transition: opacity 0.15s;
}

#login-form button:hover { opacity: 0.85; }

#login-error {
  color: var(--danger);
  font-size: 0.85rem;
  margin-top: 0.8rem;
  min-height: 1.2em;
}

#login-success {
  color: var(--accent);
  font-size: 0.95rem;
  margin-top: 1rem;
}

#login-success.hidden { display: none; }

body.locked header,
body.locked main {
  display: none;
}

/* Header */
header {
  padding: 0.6rem 1.2rem;
  background: var(--bg);
  border-bottom: 1px solid var(--border);
}

.header-row {
  display: flex;
  align-items: center;
  gap: 1.2rem;
}

header h1 {
  font-size: 1.1rem;
  font-weight: 700;
  letter-spacing: -0.3px;
  white-space: nowrap;
  flex-shrink: 0;
}

header h1 span {
  color: var(--accent);
}

.overall-progress {
  flex: 1;
  max-width: 300px;
}

.overall-progress .label {
  display: flex;
  justify-content: space-between;
  font-size: 0.72rem;
  color: var(--text-dim);
  margin-bottom: 0.2rem;
}

.progress-bar {
  height: 8px;
  background: var(--progress-bg);
  border-radius: 4px;
  overflow: hidden;
}

.progress-bar .fill {
  height: 100%;
  background: var(--accent);
  border-radius: 4px;
  transition: width 0.4s ease;
  box-shadow: 0 0 8px var(--accent-glow);
}

/* Main content */
main {
  max-width: 900px;
  margin: 0 auto;
  padding: 1rem 1rem 4rem;
}

/* Getting Started banner */
.getting-started {
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: 10px;
  padding: 1.2rem 1.5rem;
  margin-bottom: 2rem;
  display: flex;
  align-items: center;
  gap: 1rem;
  cursor: pointer;
  transition: border-color 0.2s;
}

.getting-started:hover {
  border-color: var(--accent);
}

.getting-started .icon {
  font-size: 1.5rem;
  flex-shrink: 0;
}

.getting-started .info h3 {
  font-size: 1rem;
  font-weight: 600;
}

.getting-started .info p {
  font-size: 0.85rem;
  color: var(--text-dim);
}

/* Unit cards */
.unit-card {
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: 12px;
  margin-bottom: 1rem;
  overflow: hidden;
  transition: border-color 0.2s;
}

.unit-card:hover {
  border-color: var(--accent);
}

.unit-header {
  padding: 1.2rem 1.5rem;
  cursor: pointer;
  display: flex;
  align-items: center;
  gap: 1rem;
  user-select: none;
}

.unit-number {
  width: 44px;
  height: 44px;
  border-radius: 10px;
  background: var(--accent-dim);
  color: var(--accent);
  display: flex;
  align-items: center;
  justify-content: center;
  font-weight: 700;
  font-size: 1.2rem;
  flex-shrink: 0;
}

.unit-info {
  flex: 1;
}

.unit-info h2 {
  font-size: 1.1rem;
  font-weight: 600;
  margin-bottom: 0.15rem;
}

.unit-info .unit-subtitle {
  font-size: 0.85rem;
  color: var(--text-dim);
}

.unit-progress {
  width: 100px;
  text-align: right;
  flex-shrink: 0;
}

.unit-progress .count {
  font-size: 0.8rem;
  color: var(--text-dim);
  margin-bottom: 0.3rem;
}

.unit-progress .progress-bar {
  height: 6px;
}

.chevron {
  color: var(--text-dim);
  font-size: 1.2rem;
  transition: transform 0.3s ease;
  flex-shrink: 0;
}

.unit-card.expanded .chevron {
  transform: rotate(90deg);
}

/* Lesson list */
.unit-body {
  display: none;
  border-top: 1px solid var(--border);
  padding: 0.5rem 0;
}

.unit-card.expanded .unit-body {
  display: block;
}

.lesson {
  padding: 0.8rem 1.5rem 0.8rem 1.5rem;
}

.lesson + .lesson {
  border-top: 1px solid var(--border);
}

.lesson-header {
  display: flex;
  align-items: center;
  gap: 0.75rem;
}

.lesson-check {
  width: 36px;
  height: 36px;
  min-width: 36px;
  border: 2px solid var(--border);
  border-radius: 5px;
  cursor: pointer;
  display: flex;
  align-items: center;
  justify-content: center;
  flex-shrink: 0;
  transition: all 0.2s;
  -webkit-tap-highlight-color: transparent;
}

.lesson-check:hover {
  border-color: var(--accent);
}

.lesson-check.checked {
  background: var(--accent);
  border-color: var(--accent);
}

.lesson-check.checked::after {
  content: '\2713';
  color: var(--bg);
  font-size: 0.85rem;
  font-weight: 700;
}

.lesson-title {
  font-weight: 500;
  font-size: 0.95rem;
  flex: 1;
}

.lesson.completed .lesson-title {
  color: var(--text-dim);
  text-decoration: line-through;
  text-decoration-color: var(--text-dim);
}

/* Resource links */
.lesson-resources {
  margin-top: 0.5rem;
  padding-left: 2.75rem;
  display: flex;
  flex-wrap: wrap;
  gap: 0.4rem;
}

.resource-link {
  display: inline-flex;
  align-items: center;
  gap: 0.35rem;
  padding: 0.5rem 0.9rem;
  min-height: 44px;
  border-radius: 6px;
  font-size: 0.85rem;
  text-decoration: none;
  color: var(--text);
  background: var(--bg);
  border: 1px solid var(--border);
  transition: all 0.15s;
  white-space: nowrap;
  -webkit-tap-highlight-color: transparent;
}

.resource-link:hover {
  border-color: var(--accent);
  color: var(--accent);
}

.resource-link .icon {
  font-size: 0.9rem;
}

.resource-link.slideshow { border-left: 3px solid var(--accent); }
.resource-link.activity { border-left: 3px solid var(--warning); }
.resource-link.build-guide { border-left: 3px solid var(--danger); }
.resource-link.video { border-left: 3px solid var(--video); }
.resource-link.programming { border-left: 3px solid var(--code); }
.resource-link.reference { border-left: 3px solid var(--text-dim); }

/* Video embeds */
.video-container {
  margin-top: 0.5rem;
  margin-left: 2.75rem;
  max-width: 480px;
}

.video-container video {
  width: 100%;
  border-radius: 8px;
  border: 1px solid var(--border);
}

/* Section dividers within unit body */
.section-label {
  padding: 0.6rem 1.5rem 0.2rem;
  font-size: 0.75rem;
  font-weight: 600;
  text-transform: uppercase;
  letter-spacing: 0.08em;
  color: var(--text-dim);
}

/* Reset progress button */
.reset-section {
  text-align: center;
  padding: 2rem 0;
}

.reset-btn {
  background: transparent;
  border: 1px solid var(--border);
  color: var(--text-dim);
  padding: 0.5rem 1.2rem;
  border-radius: 6px;
  cursor: pointer;
  font-size: 0.85rem;
  transition: all 0.2s;
}

.reset-btn:hover {
  border-color: var(--danger);
  color: var(--danger);
}

/* Getting Started panel */
.gs-panel {
  display: none;
  border-top: 1px solid var(--border);
  padding: 1rem 1.5rem;
}

.getting-started.expanded .gs-panel {
  display: block;
}

.getting-started.expanded {
  flex-wrap: wrap;
}

.gs-panel .resource-link {
  margin: 0.2rem;
}

/* ============ Content Viewer Modal ============ */
.viewer-overlay {
  display: none;
  position: fixed;
  top: 0;
  right: 0;
  bottom: 0;
  left: var(--chat-width, 33.33vw);
  z-index: 1000;
  background: rgba(0, 0, 0, 0.92);
  justify-content: center;
  align-items: center;
}

.viewer-overlay.active {
  display: flex;
}

.viewer-container {
  position: relative;
  width: 96%;
  max-width: 1100px;
  height: 94vh;
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: 12px;
  overflow: hidden;
  display: flex;
  flex-direction: column;
}

.viewer-header {
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: 0.7rem 1rem;
  border-bottom: 1px solid var(--border);
  flex-shrink: 0;
  background: var(--bg);
}

.viewer-title {
  font-size: 0.9rem;
  font-weight: 600;
  color: var(--text);
  overflow: hidden;
  text-overflow: ellipsis;
  white-space: nowrap;
}

.viewer-close {
  background: transparent;
  border: 1px solid var(--border);
  color: var(--text-dim);
  width: 44px;
  height: 44px;
  border-radius: 6px;
  cursor: pointer;
  font-size: 1.1rem;
  display: flex;
  align-items: center;
  justify-content: center;
  flex-shrink: 0;
  transition: all 0.15s;
}

.viewer-close:hover {
  border-color: var(--danger);
  color: var(--danger);
}

.viewer-body {
  flex: 1;
  overflow: auto;
  position: relative;
}

/* Document viewer */
.viewer-body .doc-content {
  padding: 2rem 2.5rem;
  max-width: 800px;
  margin: 0 auto;
  font-size: 0.95rem;
  line-height: 1.7;
  color: var(--text);
}

.doc-content h1, .doc-content h2, .doc-content h3, .doc-content h4 {
  color: var(--accent);
  margin: 1.5rem 0 0.5rem;
}

.doc-content h1 { font-size: 1.5rem; }
.doc-content h2 { font-size: 1.25rem; }
.doc-content h3 { font-size: 1.1rem; }

.doc-content p { margin: 0.5rem 0; }

.doc-content table {
  width: 100%;
  border-collapse: collapse;
  margin: 1rem 0;
}

.doc-content th, .doc-content td {
  border: 1px solid var(--border);
  padding: 0.6rem 0.85rem;
  text-align: left;
  font-size: 0.9rem;
}

.doc-content th {
  background: var(--bg);
  color: var(--accent);
  font-weight: 600;
}

.doc-content img {
  max-width: 100%;
  height: auto;
  border-radius: 6px;
  margin: 0.5rem 0;
}

.doc-content ul, .doc-content ol {
  margin: 0.5rem 0 0.5rem 1.5rem;
}

.doc-content li { margin: 0.3rem 0; }

/* Slideshow viewer */
.slideshow-viewer {
  display: flex;
  flex-direction: column;
  height: 100%;
  align-items: center;
  justify-content: center;
  background: #000;
  position: relative;
  user-select: none;
}

.slideshow-viewer img {
  max-width: 100%;
  max-height: calc(100% - 50px);
  object-fit: contain;
}

.slide-controls {
  position: absolute;
  bottom: 0;
  left: 0;
  right: 0;
  display: flex;
  align-items: center;
  justify-content: center;
  gap: 1rem;
  padding: 0.6rem;
  background: rgba(15, 17, 23, 0.9);
}

.slide-controls button {
  background: var(--surface);
  border: 1px solid var(--border);
  color: var(--text);
  padding: 0.5rem 1.2rem;
  min-height: 44px;
  border-radius: 6px;
  cursor: pointer;
  font-size: 0.9rem;
  transition: all 0.15s;
  -webkit-tap-highlight-color: transparent;
}

.slide-controls button:hover {
  border-color: var(--accent);
  color: var(--accent);
}

.slide-controls button:disabled {
  opacity: 0.3;
  cursor: default;
}

.slide-counter {
  color: var(--text-dim);
  font-size: 0.85rem;
  min-width: 80px;
  text-align: center;
}

/* Document iframe (interactive quizzes) */
.viewer-body .doc-iframe {
  width: 100%;
  height: 100%;
  border: none;
  background: #0f1117;
}

/* PDF viewer */
.viewer-body .pdf-embed {
  width: 100%;
  height: 100%;
  border: none;
}

/* Video viewer */
.viewer-body video {
  width: 100%;
  max-height: 100%;
  background: #000;
}

/* Image viewer */
.viewer-body .image-viewer {
  display: flex;
  align-items: center;
  justify-content: center;
  height: 100%;
  background: #000;
}

.viewer-body .image-viewer img {
  max-width: 100%;
  max-height: 100%;
  object-fit: contain;
}

/* Button styling for resource-link buttons */
button.resource-link {
  cursor: pointer;
  font-family: inherit;
}

/* ============ Skill Tree Button ============ */
.skill-tree-btn {
  padding: 0.35rem 0.9rem;
  border-radius: 6px;
  border: 1px solid var(--accent);
  background: var(--accent-dim);
  color: var(--accent);
  font-size: 0.8rem;
  font-weight: 600;
  font-family: inherit;
  cursor: pointer;
  transition: all 0.2s;
  white-space: nowrap;
  flex-shrink: 0;
}

.skill-tree-btn:hover {
  background: var(--accent);
  color: var(--bg);
}

.skill-tree-btn span {
  font-weight: 400;
  font-size: 0.8rem;
  opacity: 0.8;
  margin-left: 0.4rem;
}

/* ============ Skill Tree Overlay ============ */
.skill-tree-overlay {
  display: none;
  position: fixed;
  top: 0;
  right: 0;
  bottom: 0;
  left: var(--chat-width, 33.33vw);
  z-index: 1000;
  background: rgba(0, 0, 0, 0.92);
  justify-content: center;
  align-items: center;
}

.skill-tree-overlay.active {
  display: flex;
}

.skill-tree-container {
  width: 96%;
  max-width: 1100px;
  height: 94vh;
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: 12px;
  overflow: hidden;
  display: flex;
  flex-direction: column;
}

.skill-tree-header {
  display: flex;
  align-items: center;
  padding: 0.8rem 1.2rem;
  border-bottom: 1px solid var(--border);
  background: var(--bg);
  flex-shrink: 0;
  gap: 1rem;
}

.skill-tree-header h2 {
  font-size: 1.1rem;
  font-weight: 700;
  color: var(--accent);
  white-space: nowrap;
}

.skill-tree-legend {
  display: flex;
  gap: 0.8rem;
  flex-wrap: wrap;
  flex: 1;
  justify-content: center;
}

.legend-item {
  font-size: 0.82rem;
  color: var(--text-dim);
  display: flex;
  align-items: center;
  gap: 0.3rem;
}

.legend-dot {
  width: 10px;
  height: 10px;
  border-radius: 50%;
  flex-shrink: 0;
}

#skill-tree-close {
  background: transparent;
  border: 1px solid var(--border);
  color: var(--text-dim);
  width: 44px;
  height: 44px;
  border-radius: 6px;
  cursor: pointer;
  font-size: 1.1rem;
  display: flex;
  align-items: center;
  justify-content: center;
  flex-shrink: 0;
  transition: all 0.15s;
}

#skill-tree-close:hover {
  border-color: var(--danger);
  color: var(--danger);
}

.skill-tree-panel {
  flex: 1;
  overflow: auto;
  position: relative;
  padding: 20px;
}

.skill-tree-svg {
  position: absolute;
  top: 0;
  left: 0;
  pointer-events: none;
}

.skill-line {
  stroke: #2a2e3d;
  stroke-width: 2;
}

.skill-line.active {
  stroke: #4a5068;
  stroke-width: 2;
}

/* Skill nodes */
.skill-node {
  position: absolute;
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: center;
  cursor: pointer;
  transition: transform 0.15s;
}

.skill-node:hover {
  transform: scale(1.08);
}

.skill-node.locked {
  opacity: 0.35;
}

.skill-node.locked:hover {
  opacity: 0.5;
}

.skill-circle {
  width: 52px;
  height: 52px;
  border-radius: 50%;
  border: 3px solid;
  background: var(--surface);
  display: flex;
  align-items: center;
  justify-content: center;
  font-size: 1.4rem;
  transition: all 0.2s;
  box-shadow: 0 0 0 0 transparent;
}

.skill-node.completed .skill-circle {
  box-shadow: 0 0 12px rgba(255, 255, 255, 0.15);
}

.skill-node.available .skill-circle {
  animation: pulse-glow 2s ease-in-out infinite;
}

.skill-node.challenge .skill-circle {
  width: 56px;
  height: 56px;
  border-radius: 12px;
  border-width: 3px;
}

@keyframes pulse-glow {
  0%, 100% { box-shadow: 0 0 4px rgba(255, 255, 255, 0.1); }
  50% { box-shadow: 0 0 16px rgba(255, 255, 255, 0.25); }
}

.skill-label {
  margin-top: 4px;
  font-size: 0.78rem;
  font-weight: 600;
  color: var(--text-dim);
  text-align: center;
  line-height: 1.2;
  max-width: 120px;
  overflow: hidden;
  text-overflow: ellipsis;
}

.skill-node.completed .skill-label {
  color: var(--text);
}

/* ============ Skill Detail Popup ============ */
#skill-detail {
  position: fixed;
  inset: 0;
  z-index: 2000;
  background: rgba(0, 0, 0, 0.7);
  display: flex;
  align-items: center;
  justify-content: center;
}

.skill-detail-card {
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: 12px;
  max-width: 480px;
  width: 90%;
  overflow: hidden;
}

.skill-detail-header {
  display: flex;
  align-items: center;
  gap: 0.8rem;
  padding: 1rem 1.2rem;
  border-bottom: 3px solid;
  background: var(--bg);
}

.skill-detail-icon {
  font-size: 2rem;
}

.skill-detail-header h3 {
  font-size: 1.1rem;
  font-weight: 700;
  color: var(--text);
  margin-bottom: 0.1rem;
}

.skill-detail-branch {
  font-size: 0.75rem;
  font-weight: 600;
  text-transform: uppercase;
  letter-spacing: 0.05em;
}

.skill-detail-close {
  margin-left: auto;
  background: transparent;
  border: 1px solid var(--border);
  color: var(--text-dim);
  width: 44px;
  height: 44px;
  border-radius: 6px;
  cursor: pointer;
  font-size: 1rem;
  display: flex;
  align-items: center;
  justify-content: center;
}

.skill-detail-close:hover {
  border-color: var(--danger);
  color: var(--danger);
}

.skill-detail-body {
  padding: 1rem 1.2rem;
}

.skill-detail-state {
  display: inline-block;
  padding: 0.2rem 0.7rem;
  border-radius: 4px;
  font-size: 0.75rem;
  font-weight: 600;
  margin-bottom: 0.6rem;
}

.skill-detail-state.completed { background: #00d4aa22; color: #00d4aa; }
.skill-detail-state.available { background: #5cb8ff22; color: #5cb8ff; }
.skill-detail-state.locked { background: #2a2e3d; color: #8a90a5; }

.skill-detail-body p {
  font-size: 0.9rem;
  color: var(--text);
  line-height: 1.5;
  margin: 0.4rem 0;
}

.skill-requires {
  margin-top: 0.8rem;
  font-size: 0.8rem;
  color: var(--text-dim);
}

/* Challenge styling */
.skill-challenge {
  margin-top: 0.8rem;
  padding: 0.8rem;
  background: var(--bg);
  border-radius: 8px;
  border: 1px solid #e040fb33;
}

.skill-challenge h4 {
  font-size: 0.85rem;
  color: #e040fb;
  margin-bottom: 0.4rem;
}

.challenge-question {
  font-size: 0.85rem !important;
  color: var(--text) !important;
  line-height: 1.6 !important;
}

.challenge-try-btn, .challenge-complete-btn {
  display: block;
  width: 100%;
  margin-top: 0.5rem;
  padding: 0.5rem;
  border-radius: 6px;
  border: none;
  font-size: 0.85rem;
  font-family: inherit;
  font-weight: 600;
  cursor: pointer;
  transition: opacity 0.15s;
}

.challenge-try-btn {
  background: var(--accent);
  color: var(--bg);
}

.challenge-complete-btn {
  background: transparent;
  border: 1px solid #e040fb;
  color: #e040fb;
}

.challenge-try-btn:hover, .challenge-complete-btn:hover { opacity: 0.85; }

.challenge-done {
  color: var(--accent) !important;
  font-weight: 600;
}

.challenge-locked {
  color: var(--text-dim) !important;
  font-style: italic;
}

/* ============ AI Chat Sidebar ============ */
#chat-sidebar {
  position: fixed;
  left: 0;
  top: 0;
  bottom: 0;
  width: var(--chat-width, 33.33vw);
  background: var(--surface);
  border-right: 1px solid var(--border);
  display: none;
  flex-direction: column;
  z-index: 1100;
}

body:not(.locked) #chat-sidebar {
  display: flex;
}

body:not(.locked) header,
body:not(.locked) main {
  margin-left: var(--chat-width, 33.33vw);
}

/* Resize handle */
#chat-resize {
  position: absolute;
  top: 0;
  right: -12px;
  width: 24px;
  height: 100%;
  cursor: col-resize;
  z-index: 1110;
  touch-action: none;
}

#chat-resize::after {
  content: '';
  position: absolute;
  top: 50%;
  left: 50%;
  transform: translate(-50%, -50%);
  width: 4px;
  height: 40px;
  border-radius: 2px;
  background: var(--border);
  transition: background 0.15s;
}

#chat-resize:hover::after,
body.chat-resizing #chat-resize::after {
  background: var(--accent);
}

body.chat-resizing {
  cursor: col-resize;
  user-select: none;
}

.chat-header {
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: 0.8rem 1rem;
  border-bottom: 1px solid var(--border);
  background: var(--bg);
  flex-shrink: 0;
}

.chat-title {
  font-weight: 700;
  font-size: 1rem;
  color: var(--accent);
}

#chat-clear {
  background: transparent;
  border: 1px solid var(--border);
  color: var(--text-dim);
  width: 44px;
  height: 44px;
  border-radius: 6px;
  cursor: pointer;
  font-size: 1.1rem;
  display: flex;
  align-items: center;
  justify-content: center;
  transition: all 0.15s;
}

#chat-clear:hover {
  border-color: var(--accent);
  color: var(--accent);
}

#chat-messages {
  flex: 1;
  overflow-y: auto;
  padding: 0.8rem;
  display: flex;
  flex-direction: column;
  gap: 0.6rem;
}

.chat-msg {
  display: flex;
}

.chat-msg.user {
  justify-content: flex-end;
}

.chat-bubble {
  max-width: 90%;
  padding: 0.6rem 0.9rem;
  border-radius: 12px;
  font-size: 0.85rem;
  line-height: 1.5;
  white-space: pre-wrap;
  word-wrap: break-word;
}

.chat-msg.assistant .chat-bubble {
  background: var(--bg);
  border: 1px solid var(--border);
  color: var(--text);
  border-bottom-left-radius: 4px;
}

.chat-msg.user .chat-bubble {
  background: var(--accent);
  color: var(--bg);
  border-bottom-right-radius: 4px;
}

.chat-msg.assistant .chat-bubble strong {
  color: var(--accent);
}

.chat-ref-btn {
  display: inline-block;
  margin: 4px 2px;
  padding: 8px 12px;
  min-height: 44px;
  border-radius: 6px;
  border: 1px solid var(--accent);
  background: var(--accent-dim);
  color: var(--accent);
  font-size: 0.78rem;
  font-family: inherit;
  cursor: pointer;
  transition: all 0.15s;
  white-space: nowrap;
}

.chat-ref-btn:hover {
  background: var(--accent);
  color: var(--bg);
}

.chat-typing .chat-bubble::after {
  content: '';
  display: inline-block;
  width: 4px;
  height: 14px;
  background: var(--accent);
  margin-left: 4px;
  vertical-align: middle;
  animation: blink 0.8s infinite;
}

@keyframes blink {
  0%, 100% { opacity: 1; }
  50% { opacity: 0; }
}

#chat-input-area {
  border-top: 1px solid var(--border);
  padding: 0.6rem;
  display: flex;
  gap: 0.5rem;
  background: var(--bg);
  flex-shrink: 0;
}

#chat-input {
  flex: 1;
  resize: none;
  padding: 0.6rem 0.8rem;
  border-radius: 8px;
  border: 1px solid var(--border);
  background: var(--surface);
  color: var(--text);
  font-size: 0.85rem;
  font-family: inherit;
  line-height: 1.4;
  outline: none;
  transition: border-color 0.2s;
}

#chat-input:focus {
  border-color: var(--accent);
}

#chat-send {
  width: 44px;
  height: 44px;
  border-radius: 8px;
  border: none;
  background: var(--accent);
  color: var(--bg);
  font-size: 1rem;
  cursor: pointer;
  display: flex;
  align-items: center;
  justify-content: center;
  flex-shrink: 0;
  align-self: flex-end;
  transition: opacity 0.15s;
}

#chat-send:hover { opacity: 0.85; }

#chat-send:disabled {
  opacity: 0.4;
  cursor: default;
}

/* ============ Touch device styles ============ */
@media (hover: none) and (pointer: coarse) {
  /* Activate hover styles on tap via :active */
  .resource-link:active { border-color: var(--accent); color: var(--accent); }
  .unit-card:active { border-color: var(--accent); }
  .lesson-check:active { border-color: var(--accent); }
  .skill-node:active { transform: scale(1.08); }
  .getting-started:active { border-color: var(--accent); }
  .reset-btn:active { border-color: var(--danger); color: var(--danger); }
  .viewer-close:active { border-color: var(--danger); color: var(--danger); }
  .skill-tree-btn:active { background: var(--accent); color: var(--bg); }
  .slide-controls button:active { border-color: var(--accent); color: var(--accent); }
  #chat-clear:active { border-color: var(--accent); color: var(--accent); }
  .chat-ref-btn:active { background: var(--accent); color: var(--bg); }
}

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

/* Tablet landscape & portrait (768px–1024px) */
@media (max-width: 1024px) {
  :root { --chat-width: 280px; }
  .chat-bubble { font-size: 0.88rem; }
  #chat-input { font-size: 0.88rem; }
  .viewer-overlay { left: var(--chat-width, 280px); }
  .skill-tree-overlay { left: var(--chat-width, 280px); }
}

/* Tablet portrait */
@media (max-width: 820px) {
  :root { --chat-width: 260px; }
  header h1 { font-size: 1rem; }
  .overall-progress { max-width: 200px; }
}

@media (max-width: 600px) {
  header h1 { font-size: 1.6rem; }
  .unit-header { padding: 1rem; }
  .lesson { padding: 0.7rem 1rem; }
  .lesson-resources { padding-left: 2.25rem; }
  .unit-progress { width: 70px; }
  #chat-sidebar {
    width: 100%;
    height: 50vh;
    top: auto;
    bottom: 0;
    border-right: none;
    border-top: 1px solid var(--border);
  }
  body:not(.locked) #login-gate ~ header,
  body:not(.locked) #login-gate ~ main {
    margin-left: 0;
    padding-bottom: 52vh;
  }
  .viewer-overlay { left: 0; }
  .skill-tree-overlay { left: 0; }
}