/* CSS Variables */
:root {
  --primary: #22c55e;
  --primary-dark: #16a34a;
  --secondary: #3b82f6;
  --danger: #ef4444;
  --warning: #f59e0b;
  --gray-50: #f9fafb;
  --gray-100: #f3f4f6;
  --gray-200: #e5e7eb;
  --gray-300: #d1d5db;
  --gray-400: #9ca3af;
  --gray-500: #6b7280;
  --gray-600: #4b5563;
  --gray-700: #374151;
  --gray-800: #1f2937;
  --gray-900: #111827;
  --radius: 8px;
  --shadow: 0 1px 3px rgba(0,0,0,0.1);
  --shadow-lg: 0 4px 6px rgba(0,0,0,0.1);
}

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

body {
  font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, Oxygen, Ubuntu, sans-serif;
  background: var(--gray-50);
  color: var(--gray-800);
  line-height: 1.5;
  min-height: 100vh;
}

/* Navigation */
.nav {
  background: white;
  border-bottom: 1px solid var(--gray-200);
  padding: 0.75rem 1rem;
  display: flex;
  align-items: center;
  justify-content: space-between;
  position: sticky;
  top: 0;
  z-index: 100;
}

.nav-brand {
  font-size: 1.25rem;
  font-weight: 700;
  color: var(--primary-dark);
}

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

.nav-btn {
  padding: 0.5rem 1rem;
  border: none;
  background: transparent;
  color: var(--gray-600);
  font-size: 0.875rem;
  font-weight: 500;
  border-radius: var(--radius);
  cursor: pointer;
  transition: all 0.2s;
}

.nav-btn:hover {
  background: var(--gray-100);
  color: var(--gray-800);
}

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

/* Views */
.view {
  display: none;
  padding: 1rem;
  max-width: 1200px;
  margin: 0 auto;
}

.view.active {
  display: block;
}

.view-header {
  display: flex;
  justify-content: space-between;
  align-items: center;
  margin-bottom: 1.5rem;
}

h1 {
  font-size: 1.5rem;
  font-weight: 700;
  color: var(--gray-900);
}

h2 {
  font-size: 1.125rem;
  font-weight: 600;
  color: var(--gray-800);
  margin: 1.5rem 0 1rem;
}

/* Stats Grid */
.stats-grid {
  display: grid;
  grid-template-columns: repeat(2, 1fr);
  gap: 1rem;
  margin-bottom: 1.5rem;
}

.stat-card {
  background: white;
  padding: 1rem;
  border-radius: var(--radius);
  box-shadow: var(--shadow);
  text-align: center;
}

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

.stat-label {
  font-size: 0.875rem;
  color: var(--gray-500);
  margin-top: 0.25rem;
}

/* Buttons */
.btn {
  padding: 0.5rem 1rem;
  border: none;
  border-radius: var(--radius);
  font-size: 0.875rem;
  font-weight: 500;
  cursor: pointer;
  transition: all 0.2s;
  display: inline-flex;
  align-items: center;
  gap: 0.5rem;
}

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

.btn-primary:hover {
  background: var(--primary-dark);
}

.btn-secondary {
  background: var(--gray-200);
  color: var(--gray-700);
}

.btn-secondary:hover {
  background: var(--gray-300);
}

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

.btn-danger:hover {
  background: #dc2626;
}

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

.back-btn {
  margin-bottom: 1rem;
}

/* Search */
.search-bar {
  margin-bottom: 1rem;
}

.search-bar input {
  width: 100%;
  padding: 0.75rem 1rem;
  border: 1px solid var(--gray-200);
  border-radius: var(--radius);
  font-size: 0.875rem;
}

.search-bar input:focus {
  outline: none;
  border-color: var(--primary);
}

/* Lists */
.list-container {
  display: flex;
  flex-direction: column;
  gap: 0.75rem;
}

.empty-state {
  text-align: center;
  padding: 2rem;
  color: var(--gray-400);
  font-style: italic;
}

/* Cards */
.card {
  background: white;
  border-radius: var(--radius);
  padding: 1rem;
  box-shadow: var(--shadow);
  cursor: pointer;
  transition: box-shadow 0.2s;
}

.card:hover {
  box-shadow: var(--shadow-lg);
}

.card-header {
  display: flex;
  justify-content: space-between;
  align-items: flex-start;
  margin-bottom: 0.5rem;
}

.card-title {
  font-weight: 600;
  color: var(--gray-900);
}

.card-subtitle {
  font-size: 0.875rem;
  color: var(--gray-500);
}

.card-actions {
  display: flex;
  gap: 0.5rem;
  margin-top: 0.75rem;
}

/* Badges */
.badge {
  display: inline-block;
  padding: 0.25rem 0.5rem;
  border-radius: 9999px;
  font-size: 0.75rem;
  font-weight: 500;
}

.badge-beginner {
  background: #dcfce7;
  color: #166534;
}

.badge-intermediate {
  background: #dbeafe;
  color: #1e40af;
}

.badge-advanced {
  background: #fef3c7;
  color: #92400e;
}

.badge-pro {
  background: #fce7f3;
  color: #9d174d;
}

/* Rating Stars */
.rating {
  display: flex;
  gap: 0.25rem;
}

.star {
  color: var(--warning);
}

.star.empty {
  color: var(--gray-300);
}

/* Modals */
.modal {
  display: none;
  position: fixed;
  top: 0;
  left: 0;
  right: 0;
  bottom: 0;
  background: rgba(0,0,0,0.5);
  z-index: 200;
  align-items: flex-start;
  justify-content: center;
  padding: 1rem;
  overflow-y: auto;
}

.modal.active {
  display: flex;
}

.modal-content {
  background: white;
  border-radius: var(--radius);
  width: 100%;
  max-width: 500px;
  margin-top: 2rem;
  box-shadow: var(--shadow-lg);
}

.modal-header {
  display: flex;
  justify-content: space-between;
  align-items: center;
  padding: 1rem;
  border-bottom: 1px solid var(--gray-200);
}

.modal-header h2 {
  margin: 0;
  font-size: 1.125rem;
}

.close-btn {
  background: none;
  border: none;
  font-size: 1.5rem;
  color: var(--gray-400);
  cursor: pointer;
  line-height: 1;
}

.close-btn:hover {
  color: var(--gray-600);
}

/* Forms */
form {
  padding: 1rem;
}

.form-row {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 1rem;
}

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

.form-group label {
  display: block;
  font-size: 0.875rem;
  font-weight: 500;
  color: var(--gray-700);
  margin-bottom: 0.375rem;
}

.form-group input,
.form-group select,
.form-group textarea {
  width: 100%;
  padding: 0.5rem 0.75rem;
  border: 1px solid var(--gray-300);
  border-radius: var(--radius);
  font-size: 0.875rem;
  font-family: inherit;
}

.form-group input:focus,
.form-group select:focus,
.form-group textarea:focus {
  outline: none;
  border-color: var(--primary);
}

.form-actions {
  display: flex;
  justify-content: flex-end;
  gap: 0.75rem;
  margin-top: 1rem;
  padding-top: 1rem;
  border-top: 1px solid var(--gray-200);
}

/* Student Detail */
.student-profile {
  background: white;
  border-radius: var(--radius);
  padding: 1.5rem;
  box-shadow: var(--shadow);
  margin-bottom: 1.5rem;
}

.student-profile-header {
  display: flex;
  justify-content: space-between;
  align-items: flex-start;
  margin-bottom: 1rem;
}

.student-profile h2 {
  margin: 0 0 0.5rem;
}

.student-meta {
  display: flex;
  flex-wrap: wrap;
  gap: 1rem;
  font-size: 0.875rem;
  color: var(--gray-600);
}

.student-meta span {
  display: flex;
  align-items: center;
  gap: 0.25rem;
}

.student-notes {
  margin-top: 1rem;
  padding-top: 1rem;
  border-top: 1px solid var(--gray-200);
  font-size: 0.875rem;
  color: var(--gray-600);
}

/* Stats Section */
.student-stats {
  display: grid;
  grid-template-columns: repeat(2, 1fr);
  gap: 1rem;
  margin-bottom: 1.5rem;
}

.stat-box {
  background: var(--gray-50);
  padding: 1rem;
  border-radius: var(--radius);
  text-align: center;
}

.stat-box-value {
  font-size: 1.5rem;
  font-weight: 700;
  color: var(--primary-dark);
}

.stat-box-label {
  font-size: 0.75rem;
  color: var(--gray-500);
  text-transform: uppercase;
  letter-spacing: 0.05em;
}

/* Tabs */
.tabs {
  display: flex;
  gap: 0.5rem;
  border-bottom: 1px solid var(--gray-200);
  margin-bottom: 1rem;
}

.tab-btn {
  padding: 0.75rem 1rem;
  border: none;
  background: transparent;
  color: var(--gray-600);
  font-size: 0.875rem;
  font-weight: 500;
  cursor: pointer;
  border-bottom: 2px solid transparent;
  margin-bottom: -1px;
}

.tab-btn:hover {
  color: var(--gray-800);
}

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

.tab-content {
  display: none;
}

.tab-content.active {
  display: block;
}

/* Progress Table */
.progress-table {
  width: 100%;
  border-collapse: collapse;
  font-size: 0.875rem;
}

.progress-table th,
.progress-table td {
  padding: 0.75rem;
  text-align: left;
  border-bottom: 1px solid var(--gray-200);
}

.progress-table th {
  font-weight: 600;
  color: var(--gray-700);
  background: var(--gray-50);
}

.progress-table tr:hover {
  background: var(--gray-50);
}

/* Responsive */
@media (min-width: 768px) {
  .view {
    padding: 1.5rem;
  }
  
  .stats-grid {
    grid-template-columns: repeat(4, 1fr);
  }
  
  .student-stats {
    grid-template-columns: repeat(4, 1fr);
  }
  
  h1 {
    font-size: 1.875rem;
  }
}

@media (max-width: 480px) {
  .form-row {
    grid-template-columns: 1fr;
  }
  
  .nav-links {
    gap: 0.25rem;
  }
  
  .nav-btn {
    padding: 0.375rem 0.5rem;
    font-size: 0.75rem;
  }
}