/* ===== HỌC CÙNG CON - Hệ thống Style ===== */

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

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

body {
  font-family: 'Segoe UI', system-ui, -apple-system, sans-serif;
  line-height: 1.6;
  color: var(--text-primary);
  background: var(--bg-primary);
  min-height: 100vh;
  transition: background 0.3s, color 0.3s;
}

img, svg {
  max-width: 100%;
  display: block;
}

a {
  color: var(--accent);
  text-decoration: none;
}

a:hover {
  text-decoration: underline;
}

button {
  cursor: pointer;
  font-family: inherit;
  font-size: inherit;
}

input, select, textarea {
  font-family: inherit;
  font-size: inherit;
}

ul, ol {
  list-style: none;
}

/* ---- Theme Variables (Dark mode mặc định) ---- */
:root {
  --bg-primary: #0f0f1a;
  --bg-secondary: #1a1a2e;
  --bg-card: #16213e;
  --bg-input: #1a1a2e;
  --bg-hover: #24244a;
  --text-primary: #e8e8f0;
  --text-secondary: #a0a0b8;
  --text-muted: #6b6b80;
  --accent: #7c5cfc;
  --accent-hover: #6a4ae0;
  --accent-glow: rgba(124, 92, 252, 0.3);
  --success: #2ed573;
  --success-bg: rgba(46, 213, 115, 0.15);
  --warning: #ffa502;
  --warning-bg: rgba(255, 165, 2, 0.15);
  --danger: #ff4757;
  --danger-bg: rgba(255, 71, 87, 0.15);
  --info: #2e86de;
  --info-bg: rgba(46, 134, 222, 0.15);
  --border: #2a2a4a;
  --border-light: #3a3a5a;
  --shadow: 0 4px 20px rgba(0, 0, 0, 0.3);
  --shadow-sm: 0 2px 8px rgba(0, 0, 0, 0.2);
  --radius: 12px;
  --radius-sm: 8px;
  --radius-lg: 16px;
  --font-size-xs: 0.75rem;
  --font-size-sm: 0.875rem;
  --font-size-base: 1rem;
  --font-size-lg: 1.125rem;
  --font-size-xl: 1.25rem;
  --font-size-2xl: 1.5rem;
  --font-size-3xl: 2rem;
  --transition: 0.25s ease;
  --max-width: 1200px;
}

/* ---- Scrollbar ---- */
::-webkit-scrollbar {
  width: 8px;
  height: 8px;
}
::-webkit-scrollbar-track {
  background: var(--bg-secondary);
}
::-webkit-scrollbar-thumb {
  background: var(--border-light);
  border-radius: 4px;
}
::-webkit-scrollbar-thumb:hover {
  background: var(--text-muted);
}

/* ---- Typography ---- */
h1, h2, h3, h4, h5, h6 {
  font-weight: 700;
  line-height: 1.3;
  color: var(--text-primary);
}

h1 { font-size: var(--font-size-3xl); }
h2 { font-size: var(--font-size-2xl); }
h3 { font-size: var(--font-size-xl); }
h4 { font-size: var(--font-size-lg); }

p { margin-bottom: 0.5rem; }

/* ---- Layout ---- */
.container {
  width: 100%;
  max-width: var(--max-width);
  margin: 0 auto;
  padding: 0 1rem;
}

.flex { display: flex; }
.flex-col { flex-direction: column; }
.flex-wrap { flex-wrap: wrap; }
.items-center { align-items: center; }
.items-start { align-items: flex-start; }
.justify-center { justify-content: center; }
.justify-between { justify-content: space-between; }
.gap-xs { gap: 0.25rem; }
.gap-sm { gap: 0.5rem; }
.gap-md { gap: 1rem; }
.gap-lg { gap: 1.5rem; }
.gap-xl { gap: 2rem; }

.text-center { text-align: center; }
.text-right { text-align: right; }
.text-sm { font-size: var(--font-size-sm); }
.text-xs { font-size: var(--font-size-xs); }
.text-muted { color: var(--text-muted); }
.text-secondary { color: var(--text-secondary); }
.text-success { color: var(--success); }
.text-warning { color: var(--warning); }
.text-danger { color: var(--danger); }
.text-info { color: var(--info); }

.mt-sm { margin-top: 0.5rem; }
.mt-md { margin-top: 1rem; }
.mt-lg { margin-top: 1.5rem; }
.mt-xl { margin-top: 2rem; }
.mb-sm { margin-bottom: 0.5rem; }
.mb-md { margin-bottom: 1rem; }
.mb-lg { margin-bottom: 1.5rem; }
.mb-xl { margin-bottom: 2rem; }

.w-full { width: 100%; }

/* ---- Card ---- */
.card {
  background: var(--bg-card);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 1.5rem;
  box-shadow: var(--shadow-sm);
  transition: transform var(--transition), box-shadow var(--transition);
}

.card:hover {
  transform: translateY(-2px);
  box-shadow: var(--shadow);
}

.card-header {
  display: flex;
  align-items: center;
  justify-content: space-between;
  margin-bottom: 1rem;
  padding-bottom: 0.75rem;
  border-bottom: 1px solid var(--border);
}

.card-body {
  color: var(--text-secondary);
}

.card-footer {
  margin-top: 1rem;
  padding-top: 0.75rem;
  border-top: 1px solid var(--border);
}

/* ---- Button ---- */
.btn {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  gap: 0.5rem;
  padding: 0.625rem 1.25rem;
  border: none;
  border-radius: var(--radius-sm);
  font-weight: 600;
  font-size: var(--font-size-sm);
  transition: all var(--transition);
  white-space: nowrap;
  user-select: none;
}

.btn:active {
  transform: scale(0.97);
}

.btn-primary {
  background: var(--accent);
  color: #fff;
}

.btn-primary:hover {
  background: var(--accent-hover);
  box-shadow: 0 0 20px var(--accent-glow);
}

.btn-secondary {
  background: var(--bg-hover);
  color: var(--text-primary);
  border: 1px solid var(--border);
}

.btn-secondary:hover {
  background: var(--border-light);
  border-color: var(--accent);
}

.btn-success {
  background: var(--success);
  color: #fff;
}

.btn-success:hover {
  background: #26c466;
  box-shadow: 0 0 20px rgba(46, 213, 115, 0.3);
}

.btn-danger {
  background: var(--danger);
  color: #fff;
}

.btn-danger:hover {
  background: #e8404f;
  box-shadow: 0 0 20px rgba(255, 71, 87, 0.3);
}

.btn-warning {
  background: var(--warning);
  color: #1a1a2e;
}

.btn-outline {
  background: transparent;
  color: var(--accent);
  border: 1px solid var(--accent);
}

.btn-outline:hover {
  background: var(--accent);
  color: #fff;
}

.btn-ghost {
  background: transparent;
  color: var(--text-secondary);
}

.btn-ghost:hover {
  background: var(--bg-hover);
  color: var(--text-primary);
}

.btn-sm {
  padding: 0.375rem 0.75rem;
  font-size: var(--font-size-xs);
}

.btn-lg {
  padding: 0.875rem 1.75rem;
  font-size: var(--font-size-base);
}

.btn-icon {
  width: 2.5rem;
  height: 2.5rem;
  padding: 0;
  border-radius: 50%;
}

.btn:disabled {
  opacity: 0.5;
  cursor: not-allowed;
  transform: none;
}

/* ---- Input ---- */
.input-group {
  display: flex;
  flex-direction: column;
  gap: 0.375rem;
}

.input-group label {
  font-size: var(--font-size-sm);
  font-weight: 600;
  color: var(--text-secondary);
}

.input {
  width: 100%;
  padding: 0.75rem 1rem;
  background: var(--bg-input);
  border: 1px solid var(--border);
  border-radius: var(--radius-sm);
  color: var(--text-primary);
  transition: border-color var(--transition), box-shadow var(--transition);
  outline: none;
}

.input:focus {
  border-color: var(--accent);
  box-shadow: 0 0 0 3px var(--accent-glow);
}

.input::placeholder {
  color: var(--text-muted);
}

.input-error {
  border-color: var(--danger);
}

.input-error:focus {
  box-shadow: 0 0 0 3px var(--danger-bg);
}

select.input {
  appearance: none;
  background-image: url("data:image/svg+xml,%3Csvg xmlns='http://www.w3.org/2000/svg' width='12' height='12' fill='%23a0a0b8' viewBox='0 0 16 16'%3E%3Cpath d='M8 11L3 6h10z'/%3E%3C/svg%3E");
  background-repeat: no-repeat;
  background-position: right 0.75rem center;
  padding-right: 2rem;
}

textarea.input {
  min-height: 100px;
  resize: vertical;
}

/* ---- Badge ---- */
.badge {
  display: inline-flex;
  align-items: center;
  gap: 0.25rem;
  padding: 0.2rem 0.625rem;
  border-radius: 999px;
  font-size: var(--font-size-xs);
  font-weight: 600;
  white-space: nowrap;
}

.badge-primary {
  background: var(--accent-glow);
  color: var(--accent);
}

.badge-success {
  background: var(--success-bg);
  color: var(--success);
}

.badge-warning {
  background: var(--warning-bg);
  color: var(--warning);
}

.badge-danger {
  background: var(--danger-bg);
  color: var(--danger);
}

.badge-info {
  background: var(--info-bg);
  color: var(--info);
}

/* ---- Modal ---- */
.modal-overlay {
  position: fixed;
  inset: 0;
  background: rgba(0, 0, 0, 0.7);
  backdrop-filter: blur(4px);
  display: flex;
  align-items: center;
  justify-content: center;
  z-index: 1000;
  padding: 1rem;
  opacity: 0;
  visibility: hidden;
  transition: opacity 0.3s, visibility 0.3s;
}

.modal-overlay.active {
  opacity: 1;
  visibility: visible;
}

.modal {
  background: var(--bg-secondary);
  border: 1px solid var(--border);
  border-radius: var(--radius-lg);
  width: 100%;
  max-width: 600px;
  max-height: 90vh;
  overflow-y: auto;
  box-shadow: var(--shadow);
  transform: scale(0.95) translateY(20px);
  transition: transform 0.3s;
}

.modal-overlay.active .modal {
  transform: scale(1) translateY(0);
}

.modal-header {
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: 1.25rem 1.5rem;
  border-bottom: 1px solid var(--border);
}

.modal-header h2, .modal-header h3 {
  font-size: var(--font-size-xl);
}

.modal-close {
  width: 2rem;
  height: 2rem;
  display: flex;
  align-items: center;
  justify-content: center;
  background: var(--bg-hover);
  border: none;
  border-radius: 50%;
  color: var(--text-secondary);
  font-size: 1.25rem;
  transition: all var(--transition);
}

.modal-close:hover {
  background: var(--border-light);
  color: var(--text-primary);
}

.modal-body {
  padding: 1.5rem;
}

.modal-footer {
  display: flex;
  align-items: center;
  justify-content: flex-end;
  gap: 0.75rem;
  padding: 1rem 1.5rem;
  border-top: 1px solid var(--border);
}

/* ---- Stage/Layer ---- */
.stage {
  display: none;
  animation: fadeIn 0.4s ease;
}

.stage.active {
  display: block;
}

/* ---- Alert / Toast ---- */
.alert {
  padding: 0.75rem 1rem;
  border-radius: var(--radius-sm);
  font-size: var(--font-size-sm);
  margin-bottom: 1rem;
}

.alert-error {
  background: var(--danger-bg);
  color: var(--danger);
  border: 1px solid rgba(255, 71, 87, 0.3);
}

.alert-success {
  background: var(--success-bg);
  color: var(--success);
  border: 1px solid rgba(46, 213, 115, 0.3);
}

.alert-info {
  background: var(--info-bg);
  color: var(--info);
  border: 1px solid rgba(46, 134, 222, 0.3);
}

.toast-container {
  position: fixed;
  top: 1rem;
  right: 1rem;
  z-index: 9999;
  display: flex;
  flex-direction: column;
  gap: 0.5rem;
}

.toast {
  padding: 0.75rem 1.25rem;
  border-radius: var(--radius-sm);
  font-size: var(--font-size-sm);
  font-weight: 500;
  box-shadow: var(--shadow);
  animation: slideInRight 0.3s ease;
  max-width: 360px;
}

.toast-success { background: var(--success); color: #fff; }
.toast-error { background: var(--danger); color: #fff; }
.toast-info { background: var(--info); color: #fff; }
.toast-warning { background: var(--warning); color: #1a1a2e; }

/* ---- Skeleton loading ---- */
.skeleton {
  background: linear-gradient(90deg, var(--bg-card) 25%, var(--bg-hover) 50%, var(--bg-card) 75%);
  background-size: 200% 100%;
  animation: shimmer 1.5s infinite;
  border-radius: var(--radius-sm);
}

.skeleton-text {
  height: 1rem;
  margin-bottom: 0.5rem;
}

.skeleton-text-sm {
  height: 0.75rem;
  width: 60%;
}

/* ---- Header ---- */
.header {
  background: var(--bg-secondary);
  border-bottom: 1px solid var(--border);
  padding: 0.75rem 0;
  position: sticky;
  top: 0;
  z-index: 100;
}

.header-inner {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 1rem;
}

.header-logo {
  display: flex;
  align-items: center;
  gap: 0.5rem;
  font-size: var(--font-size-xl);
  font-weight: 700;
  color: var(--text-primary);
}

.header-logo .logo-icon {
  width: 36px;
  height: 36px;
  background: var(--accent);
  border-radius: var(--radius-sm);
  display: flex;
  align-items: center;
  justify-content: center;
  font-size: 1.25rem;
  color: #fff;
}

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

/* ---- Stats Bar ---- */
.stats-bar {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(140px, 1fr));
  gap: 1rem;
  margin-bottom: 1.5rem;
}

.stat-card {
  background: var(--bg-card);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 1rem;
  text-align: center;
}

.stat-card .stat-value {
  font-size: var(--font-size-2xl);
  font-weight: 700;
  color: var(--text-primary);
}

.stat-card .stat-label {
  font-size: var(--font-size-xs);
  color: var(--text-muted);
  margin-top: 0.25rem;
}

.stat-card .stat-icon {
  font-size: 1.5rem;
  margin-bottom: 0.5rem;
}

/* ---- Progress Bar ---- */
.progress-bar {
  width: 100%;
  height: 8px;
  background: var(--bg-hover);
  border-radius: 999px;
  overflow: hidden;
}

.progress-bar-fill {
  height: 100%;
  background: var(--accent);
  border-radius: 999px;
  transition: width 0.5s ease;
}

.progress-bar-fill.success { background: var(--success); }
.progress-bar-fill.warning { background: var(--warning); }
.progress-bar-fill.danger { background: var(--danger); }

/* ---- Knowledge Graph / Tree ---- */
.graph-container {
  background: var(--bg-card);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 1.5rem;
  min-height: 400px;
  overflow-x: auto;
}

.graph-tree {
  display: flex;
  flex-direction: column;
  gap: 0.5rem;
  padding-left: 1.5rem;
}

.graph-node {
  display: flex;
  align-items: center;
  gap: 0.75rem;
  padding: 0.75rem 1rem;
  background: var(--bg-input);
  border: 1px solid var(--border);
  border-radius: var(--radius-sm);
  cursor: pointer;
  transition: all var(--transition);
  position: relative;
}

.graph-node::before {
  content: '';
  position: absolute;
  left: -1.5rem;
  top: -0.5rem;
  bottom: 50%;
  width: 1rem;
  border-left: 2px solid var(--border-light);
  border-bottom: 2px solid var(--border-light);
}

.graph-node:last-child::before {
  bottom: auto;
  height: calc(100% - 0.5rem);
}

.graph-node-root::before {
  display: none;
}

.graph-node:hover {
  border-color: var(--accent);
  background: var(--bg-hover);
  transform: translateX(4px);
}

.graph-node.status-locked {
  opacity: 0.5;
  cursor: not-allowed;
}

.graph-node.status-available {
  border-color: var(--info);
}

.graph-node.status-learning {
  border-color: var(--warning);
  background: var(--warning-bg);
}

.graph-node.status-done {
  border-color: var(--success);
  background: var(--success-bg);
}

.graph-node.status-mastered {
  border-color: var(--accent);
  background: var(--accent-glow);
}

.node-icon {
  width: 32px;
  height: 32px;
  border-radius: 50%;
  display: flex;
  align-items: center;
  justify-content: center;
  font-size: 1rem;
  flex-shrink: 0;
}

.node-icon.locked { background: var(--bg-hover); color: var(--text-muted); }
.node-icon.available { background: var(--info-bg); color: var(--info); }
.node-icon.learning { background: var(--warning-bg); color: var(--warning); }
.node-icon.done { background: var(--success-bg); color: var(--success); }
.node-icon.mastered { background: var(--accent-glow); color: var(--accent); }

.node-info {
  flex: 1;
  min-width: 0;
}

.node-info .node-title {
  font-weight: 600;
  font-size: var(--font-size-sm);
  color: var(--text-primary);
  white-space: nowrap;
  overflow: hidden;
  text-overflow: ellipsis;
}

.node-info .node-desc {
  font-size: var(--font-size-xs);
  color: var(--text-muted);
}

/* ---- Quiz ---- */
.quiz-question {
  margin-bottom: 1.5rem;
}

.quiz-question h4 {
  margin-bottom: 0.75rem;
  font-size: var(--font-size-base);
}

.quiz-options {
  display: flex;
  flex-direction: column;
  gap: 0.5rem;
}

.quiz-option {
  display: flex;
  align-items: center;
  gap: 0.75rem;
  padding: 0.75rem 1rem;
  background: var(--bg-input);
  border: 1px solid var(--border);
  border-radius: var(--radius-sm);
  cursor: pointer;
  transition: all var(--transition);
}

.quiz-option:hover {
  border-color: var(--accent);
  background: var(--bg-hover);
}

.quiz-option.selected {
  border-color: var(--accent);
  background: var(--accent-glow);
}

.quiz-option.correct {
  border-color: var(--success);
  background: var(--success-bg);
}

.quiz-option.wrong {
  border-color: var(--danger);
  background: var(--danger-bg);
}

.quiz-option input[type="radio"] {
  accent-color: var(--accent);
}

/* ---- Login Page ---- */
.login-page {
  min-height: 100vh;
  display: flex;
  align-items: center;
  justify-content: center;
  background: var(--bg-primary);
  padding: 1rem;
}

.login-card {
  width: 100%;
  max-width: 420px;
}

.login-logo {
  text-align: center;
  margin-bottom: 2rem;
}

.login-logo .logo-large {
  width: 72px;
  height: 72px;
  background: var(--accent);
  border-radius: var(--radius);
  display: inline-flex;
  align-items: center;
  justify-content: center;
  font-size: 2.5rem;
  margin-bottom: 1rem;
  box-shadow: 0 0 30px var(--accent-glow);
}

.login-logo h1 {
  font-size: var(--font-size-2xl);
  background: linear-gradient(135deg, var(--accent), #b794f4);
  -webkit-background-clip: text;
  -webkit-text-fill-color: transparent;
  background-clip: text;
}

.login-logo p {
  color: var(--text-muted);
  margin-top: 0.25rem;
}

.login-tabs {
  display: flex;
  margin-bottom: 1.5rem;
  border-bottom: 2px solid var(--border);
}

.login-tab {
  flex: 1;
  padding: 0.75rem;
  text-align: center;
  background: none;
  border: none;
  color: var(--text-muted);
  font-weight: 600;
  font-size: var(--font-size-sm);
  position: relative;
  cursor: pointer;
}

.login-tab.active {
  color: var(--accent);
}

.login-tab.active::after {
  content: '';
  position: absolute;
  bottom: -2px;
  left: 0;
  right: 0;
  height: 2px;
  background: var(--accent);
}

/* ---- Lesson Page ---- */
.lesson-layers {
  display: flex;
  justify-content: center;
  gap: 0.5rem;
  margin-bottom: 1.5rem;
  flex-wrap: wrap;
}

.layer-dot {
  width: 40px;
  height: 40px;
  border-radius: 50%;
  display: flex;
  align-items: center;
  justify-content: center;
  font-size: 1rem;
  background: var(--bg-hover);
  color: var(--text-muted);
  border: 2px solid var(--border);
  transition: all var(--transition);
}

.layer-dot.active {
  background: var(--accent);
  color: #fff;
  border-color: var(--accent);
  box-shadow: 0 0 12px var(--accent-glow);
}

.layer-dot.done {
  background: var(--success-bg);
  color: var(--success);
  border-color: var(--success);
}

.lesson-content {
  background: var(--bg-card);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 1.5rem;
  min-height: 300px;
}

.lesson-nav {
  display: flex;
  justify-content: space-between;
  gap: 1rem;
  margin-top: 1.5rem;
}

/* ---- Admin Page ---- */
.admin-layout {
  display: grid;
  grid-template-columns: 260px 1fr;
  min-height: 100vh;
}

.admin-sidebar {
  background: var(--bg-secondary);
  border-right: 1px solid var(--border);
  padding: 1.5rem;
}

.admin-main {
  padding: 1.5rem;
  overflow-x: auto;
}

.admin-nav-item {
  display: flex;
  align-items: center;
  gap: 0.75rem;
  padding: 0.75rem 1rem;
  border-radius: var(--radius-sm);
  color: var(--text-secondary);
  cursor: pointer;
  transition: all var(--transition);
  margin-bottom: 0.25rem;
}

.admin-nav-item:hover {
  background: var(--bg-hover);
  color: var(--text-primary);
}

.admin-nav-item.active {
  background: var(--accent-glow);
  color: var(--accent);
}

/* ---- Table ---- */
.table-container {
  overflow-x: auto;
}

table {
  width: 100%;
  border-collapse: collapse;
}

thead th {
  padding: 0.75rem 1rem;
  text-align: left;
  font-size: var(--font-size-sm);
  font-weight: 600;
  color: var(--text-muted);
  border-bottom: 2px solid var(--border);
  white-space: nowrap;
}

tbody td {
  padding: 0.75rem 1rem;
  border-bottom: 1px solid var(--border);
  font-size: var(--font-size-sm);
  color: var(--text-secondary);
}

tbody tr:hover {
  background: var(--bg-hover);
}

/* ---- Profile ---- */
.profile-header {
  display: flex;
  align-items: center;
  gap: 1.5rem;
  padding: 2rem;
  background: var(--bg-card);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  margin-bottom: 1.5rem;
}

.profile-avatar {
  width: 80px;
  height: 80px;
  border-radius: 50%;
  background: var(--accent-glow);
  display: flex;
  align-items: center;
  justify-content: center;
  font-size: 2.5rem;
  border: 3px solid var(--accent);
}

.profile-info h2 {
  font-size: var(--font-size-2xl);
}

.achievement-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(160px, 1fr));
  gap: 1rem;
}

.achievement-card {
  background: var(--bg-card);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 1rem;
  text-align: center;
}

.achievement-card .achievement-icon {
  font-size: 2rem;
  margin-bottom: 0.5rem;
}

.achievement-card .achievement-value {
  font-size: var(--font-size-xl);
  font-weight: 700;
  color: var(--text-primary);
}

.achievement-card .achievement-label {
  font-size: var(--font-size-xs);
  color: var(--text-muted);
}

/* ---- Loading Spinner ---- */
.spinner {
  width: 24px;
  height: 24px;
  border: 3px solid var(--border);
  border-top-color: var(--accent);
  border-radius: 50%;
  animation: spin 0.8s linear infinite;
}

.spinner-lg {
  width: 40px;
  height: 40px;
  border-width: 4px;
}

.loading-container {
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: center;
  gap: 1rem;
  padding: 3rem;
  color: var(--text-muted);
}

/* ---- Empty State ---- */
.empty-state {
  text-align: center;
  padding: 3rem;
  color: var(--text-muted);
}

.empty-state .empty-icon {
  font-size: 3rem;
  margin-bottom: 1rem;
}

/* ---- Animations ---- */
@keyframes fadeIn {
  from { opacity: 0; transform: translateY(8px); }
  to { opacity: 1; transform: translateY(0); }
}

@keyframes slideInRight {
  from { opacity: 0; transform: translateX(100px); }
  to { opacity: 1; transform: translateX(0); }
}

@keyframes slideInUp {
  from { opacity: 0; transform: translateY(20px); }
  to { opacity: 1; transform: translateY(0); }
}

@keyframes spin {
  to { transform: rotate(360deg); }
}

@keyframes shimmer {
  0% { background-position: -200% 0; }
  100% { background-position: 200% 0; }
}

@keyframes pulse {
  0%, 100% { opacity: 1; }
  50% { opacity: 0.5; }
}

@keyframes bounceIn {
  0% { transform: scale(0.3); opacity: 0; }
  50% { transform: scale(1.05); }
  70% { transform: scale(0.95); }
  100% { transform: scale(1); opacity: 1; }
}

.animate-fadeIn { animation: fadeIn 0.4s ease; }
.animate-slideInUp { animation: slideInUp 0.4s ease; }
.animate-bounceIn { animation: bounceIn 0.5s ease; }
.animate-pulse { animation: pulse 1.5s infinite; }

/* ---- Confetti / Badge unlock ---- */
.confetti-container {
  position: fixed;
  inset: 0;
  pointer-events: none;
  z-index: 9999;
  overflow: hidden;
}

.confetti-piece {
  position: absolute;
  width: 10px;
  height: 10px;
  animation: confettiFall linear forwards;
}

@keyframes confettiFall {
  0% { transform: translateY(-10vh) rotate(0deg); opacity: 1; }
  100% { transform: translateY(110vh) rotate(720deg); opacity: 0; }
}

.badge-unlock {
  text-align: center;
  padding: 2rem;
}

.badge-unlock .badge-icon {
  font-size: 4rem;
  animation: bounceIn 0.5s ease;
  margin-bottom: 1rem;
}

.badge-unlock h3 {
  color: var(--accent);
  margin-bottom: 0.5rem;
}

/* ---- Responsive ---- */
@media (max-width: 768px) {
  html { font-size: 15px; }

  .header-inner { flex-wrap: wrap; }
  .header-controls { width: 100%; justify-content: flex-end; }

  .admin-layout {
    grid-template-columns: 1fr;
  }

  .admin-sidebar {
    display: none;
  }

  .admin-sidebar.mobile-open {
    display: block;
    position: fixed;
    inset: 0;
    z-index: 200;
    background: var(--bg-secondary);
  }

  .profile-header {
    flex-direction: column;
    text-align: center;
  }

  .stats-bar {
    grid-template-columns: repeat(2, 1fr);
  }

  .modal {
    max-width: 100%;
    max-height: 100vh;
    border-radius: 0;
  }

  .modal-overlay {
    padding: 0;
  }

  .lesson-nav {
    flex-direction: column;
  }

  .lesson-nav .btn {
    width: 100%;
  }

  .login-card {
    padding: 1rem;
  }

  .graph-node {
    padding: 0.5rem 0.75rem;
  }
}

@media (max-width: 480px) {
  html { font-size: 14px; }

  .stats-bar {
    grid-template-columns: 1fr 1fr;
    gap: 0.5rem;
  }

  .stat-card {
    padding: 0.75rem;
  }

  .achievement-grid {
    grid-template-columns: repeat(2, 1fr);
  }

  .header-controls {
    gap: 0.5rem;
  }

  .card {
    padding: 1rem;
  }
}

/* ---- Print ---- */
@media print {
  body {
    background: #fff;
    color: #000;
  }
  .header, .modal-overlay, .toast-container {
    display: none;
  }
}