:root {
  --primary: #1a365d;
  --primary-light: #2a4a7a;
  --secondary: #2d3748;
  --accent: #3182ce;
  --success: #38a169;
  --warning: #d69e2e;
  --danger: #e53e3e;
  --bg: #f7fafc;
  --card-bg: #ffffff;
  --text: #1a202c;
  --text-muted: #718096;
  --border: #e2e8f0;
}

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

body {
  font-family: system-ui, -apple-system, sans-serif;
  background: var(--bg);
  color: var(--text);
  line-height: 1.5;
}

.container {
  max-width: 1200px;
  margin: 0 auto;
  padding: 1rem;
}

/* Header */
.header {
  background: var(--primary);
  color: white;
  padding: 1rem;
  display: flex;
  align-items: center;
  justify-content: space-between;
}

.header-logo {
  display: flex;
  align-items: center;
  gap: 1rem;
}

.header-logo img {
  height: 48px;
  width: auto;
}

.header-logo .logo-text {
  font-size: 1.5rem;
  font-weight: 700;
  letter-spacing: 1px;
}

.header-nav {
  display: flex;
  gap: 0.5rem;
}

.header-nav .btn {
  background: transparent;
  border: 1px solid rgba(255,255,255,0.3);
  color: white;
}

.header-nav .btn:hover {
  background: rgba(255,255,255,0.1);
}

/* Cards */
.card {
  background: var(--card-bg);
  border: 1px solid var(--border);
  padding: 1.5rem;
  margin-bottom: 1rem;
}

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

.card-title {
  font-size: 1.25rem;
  font-weight: 600;
}

/* Forms */
.form-group {
  margin-bottom: 1rem;
}

.form-group label {
  display: block;
  margin-bottom: 0.25rem;
  font-weight: 500;
  font-size: 0.875rem;
}

input, select, textarea {
  padding: 0.625rem;
  border: 1px solid #cbd5e0;
  border-radius: 2px;
  width: 100%;
  font-size: 1rem;
  font-family: inherit;
}

input:focus, select:focus, textarea:focus {
  outline: none;
  border-color: var(--accent);
  box-shadow: 0 0 0 2px rgba(49, 130, 206, 0.2);
}

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

/* Buttons */
.btn {
  padding: 0.625rem 1.25rem;
  border: none;
  border-radius: 2px;
  cursor: pointer;
  font-size: 0.875rem;
  font-weight: 500;
  display: inline-flex;
  align-items: center;
  gap: 0.5rem;
  transition: background 0.15s;
}

.btn:disabled {
  opacity: 0.6;
  cursor: not-allowed;
}

.btn-primary {
  background: var(--primary);
  color: white;
}

.btn-primary:hover:not(:disabled) {
  background: var(--primary-light);
}

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

.btn-success:hover:not(:disabled) {
  background: #2f855a;
}

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

.btn-danger:hover:not(:disabled) {
  background: #c53030;
}

.btn-secondary {
  background: var(--secondary);
  color: white;
}

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

.btn-outline:hover:not(:disabled) {
  background: var(--bg);
}

.btn-sm {
  padding: 0.375rem 0.75rem;
  font-size: 0.8125rem;
}

.btn-lg {
  padding: 0.75rem 1.5rem;
  font-size: 1rem;
}

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

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

th, td {
  padding: 0.75rem;
  text-align: left;
  border-bottom: 1px solid var(--border);
}

th {
  background: var(--bg);
  font-weight: 600;
  font-size: 0.8125rem;
  text-transform: uppercase;
  letter-spacing: 0.5px;
}

tr:hover {
  background: rgba(0,0,0,0.02);
}

/* Badges */
.badge {
  display: inline-block;
  padding: 0.25rem 0.5rem;
  font-size: 0.75rem;
  font-weight: 600;
  border-radius: 2px;
}

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

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

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

.badge-assignment {
  background: var(--accent);
  color: white;
}

.badge-student {
  background: #805ad5;
  color: white;
}

.badge-teacher {
  background: #dd6b20;
  color: white;
}

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

/* Utility Classes */
.text-muted { color: var(--text-muted); }
.text-danger { color: var(--danger); }
.text-warning { color: var(--warning); }
.text-success { color: var(--success); }

/* Alerts */
.alert {
  padding: 1rem;
  border-radius: 2px;
  margin-bottom: 1rem;
}

.alert-warning {
  background: #fef9e7;
  border: 1px solid var(--warning);
  color: #744210;
}

.alert-danger {
  background: #fed7d7;
  border: 1px solid var(--danger);
  color: #742a2a;
}

.alert-success {
  background: #c6f6d5;
  border: 1px solid var(--success);
  color: #22543d;
}

/* Grid */
.grid {
  display: grid;
  gap: 1rem;
}

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

.grid-3 {
  grid-template-columns: repeat(3, 1fr);
}

.grid-4 {
  grid-template-columns: repeat(4, 1fr);
}

/* Source Cards */
.source-card {
  display: flex;
  flex-direction: column;
  gap: 0.75rem;
}

.source-card .source-title {
  font-size: 1.125rem;
  font-weight: 600;
}

.source-card .source-meta {
  font-size: 0.8125rem;
  color: var(--text-muted);
}

.source-card .source-actions {
  display: flex;
  gap: 0.5rem;
  flex-wrap: wrap;
}

/* Comments */
.comment {
  padding: 1rem;
  border: 1px solid var(--border);
  margin-bottom: 0.75rem;
}

.comment-header {
  display: flex;
  justify-content: space-between;
  margin-bottom: 0.5rem;
}

.comment-author {
  font-weight: 600;
}

.comment-date {
  font-size: 0.75rem;
  color: var(--text-muted);
}

.comment-content {
  font-size: 0.9375rem;
}

.char-counter {
  font-size: 0.75rem;
  color: var(--text-muted);
  text-align: right;
}

.char-counter.warning {
  color: var(--warning);
}

.char-counter.danger {
  color: var(--danger);
}

/* Reactions */
.reactions {
  display: flex;
  gap: 0.5rem;
}

.reaction-btn {
  padding: 0.25rem 0.5rem;
  font-size: 0.75rem;
  background: var(--bg);
  border: 1px solid var(--border);
  cursor: pointer;
}

.reaction-btn.active {
  background: var(--accent);
  color: white;
  border-color: var(--accent);
}

/* Auth */
.auth-container {
  max-width: 400px;
  margin: 4rem auto;
  padding: 2rem;
}

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

.auth-logo img {
  height: 80px;
}

/* Tabs */
.tabs {
  display: flex;
  border-bottom: 1px solid var(--border);
  margin-bottom: 1rem;
}

.tab {
  padding: 0.75rem 1.25rem;
  border: none;
  background: none;
  cursor: pointer;
  font-size: 0.875rem;
  font-weight: 500;
  color: var(--text-muted);
  border-bottom: 2px solid transparent;
}

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

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

/* Modal */
.modal-overlay {
  position: fixed;
  top: 0;
  left: 0;
  right: 0;
  bottom: 0;
  background: rgba(0,0,0,0.5);
  display: none;
  align-items: center;
  justify-content: center;
  z-index: 1000;
}

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

.modal {
  background: var(--card-bg);
  max-width: 500px;
  width: 90%;
  max-height: 90vh;
  overflow-y: auto;
  padding: 1.5rem;
}

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

.modal-close {
  background: none;
  border: none;
  font-size: 1.5rem;
  cursor: pointer;
  color: var(--text-muted);
}

/* Notifications */
.notification-bell {
  position: relative;
}

.notification-count {
  position: absolute;
  top: -5px;
  right: -5px;
  background: var(--danger);
  color: white;
  font-size: 0.625rem;
  padding: 0.125rem 0.375rem;
  border-radius: 999px;
}

.notification-item {
  padding: 0.75rem;
  border-bottom: 1px solid var(--border);
}

.notification-item.unread {
  background: rgba(49, 130, 206, 0.1);
}

/* Stats */
.stat-card {
  text-align: center;
  padding: 1.5rem;
}

.stat-value {
  font-size: 2rem;
  font-weight: 700;
  color: var(--accent);
}

.stat-label {
  font-size: 0.875rem;
  color: var(--text-muted);
}

/* Empty State */
.empty-state {
  text-align: center;
  padding: 3rem 1rem;
  color: var(--text-muted);
}

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

/* Loading */
.loading {
  text-align: center;
  padding: 2rem;
  color: var(--text-muted);
}

.spinner {
  border: 2px solid var(--border);
  border-top-color: var(--accent);
  border-radius: 50%;
  width: 32px;
  height: 32px;
  animation: spin 0.8s linear infinite;
  margin: 0 auto 1rem;
}

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

/* Hidden utility */
.hidden {
  display: none !important;
}

/* Responsive */
@media (max-width: 768px) {
  .container {
    padding: 0.5rem;
  }

  .card {
    padding: 1rem;
  }

  .grid-2, .grid-3, .grid-4 {
    grid-template-columns: 1fr;
  }

  .header {
    flex-direction: column;
    gap: 1rem;
  }

  .header-nav {
    width: 100%;
    justify-content: center;
  }

  .table-container {
    font-size: 0.8125rem;
  }

  th, td {
    padding: 0.5rem;
  }

  .btn {
    padding: 0.5rem 1rem;
  }
}

@media (max-width: 480px) {
  .auth-container {
    margin: 2rem auto;
    padding: 1rem;
  }

  .card-header {
    flex-direction: column;
    gap: 0.5rem;
    align-items: flex-start;
  }
}