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

:root {
  --primary-color: #2563eb;
  --primary-dark: #1d4ed8;
  --secondary-color: #64748b;
  --success-color: #22c55e;
  --danger-color: #ef4444;
  --warning-color: #f59e0b;
  --background-color: #f8fafc;
  --card-background: #ffffff;
  --text-color: #1e293b;
  --text-muted: #64748b;
  --border-color: #e2e8f0;
  --shadow: 0 1px 3px rgba(0,0,0,0.1);
  --shadow-lg: 0 10px 15px -3px rgba(0,0,0,0.1);
}

body {
  font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, sans-serif;
  background-color: var(--background-color);
  color: var(--text-color);
  line-height: 1.6;
}

.container {
  max-width: 1200px;
  margin: 0 auto;
  padding: 0 20px;
}

/* Header */
header {
  background: var(--card-background);
  padding: 20px 0;
  box-shadow: var(--shadow);
  margin-bottom: 30px;
}

header .container,
header {
  display: flex;
  justify-content: space-between;
  align-items: center;
  max-width: 1200px;
  margin: 0 auto;
  padding: 20px;
}

header h1 {
  font-size: 24px;
  color: var(--primary-color);
}

nav {
  display: flex;
  gap: 20px;
}

nav a {
  text-decoration: none;
  color: var(--text-muted);
  font-weight: 500;
  padding: 8px 16px;
  border-radius: 6px;
  transition: all 0.2s;
}

nav a:hover,
nav a.active {
  color: var(--primary-color);
  background-color: #eff6ff;
}

/* User Info in Nav */
.user-info {
  display: flex;
  align-items: center;
  gap: 12px;
  margin-left: 20px;
  padding-left: 20px;
  border-left: 1px solid var(--border-color);
}

.user-info .username {
  color: var(--text-muted);
  font-size: 14px;
}

.logout-btn {
  text-decoration: none;
  color: var(--danger-color);
  font-weight: 500;
  padding: 6px 12px;
  border-radius: 4px;
  font-size: 14px;
  transition: all 0.2s;
}

.logout-btn:hover {
  background-color: #fef2f2;
}

/* Cards */
.card {
  background: var(--card-background);
  border-radius: 12px;
  box-shadow: var(--shadow);
  padding: 24px;
  margin-bottom: 24px;
}

.card h2 {
  font-size: 18px;
  margin-bottom: 16px;
  color: var(--text-color);
}

.card-header {
  display: flex;
  justify-content: space-between;
  align-items: center;
  margin-bottom: 16px;
}

.nested-card {
  background: var(--background-color);
  margin: 16px 0;
}

/* Forms */
.form-group {
  margin-bottom: 16px;
}

.form-group label {
  display: block;
  font-weight: 500;
  margin-bottom: 6px;
  color: var(--text-color);
}

.form-group input,
.form-group select,
.form-group textarea {
  width: 100%;
  padding: 10px 14px;
  border: 1px solid var(--border-color);
  border-radius: 8px;
  font-size: 14px;
  transition: border-color 0.2s;
}

.form-group input:focus,
.form-group select:focus,
.form-group textarea:focus {
  outline: none;
  border-color: var(--primary-color);
  box-shadow: 0 0 0 3px rgba(37, 99, 235, 0.1);
}

.form-row {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(200px, 1fr));
  gap: 16px;
  align-items: end;
}

.checkbox-group {
  display: flex;
  align-items: center;
}

.checkbox-group label {
  display: flex;
  align-items: center;
  gap: 8px;
  cursor: pointer;
  margin-bottom: 0;
}

.checkbox-group input[type="checkbox"] {
  width: 18px;
  height: 18px;
  cursor: pointer;
}

/* Buttons */
.btn {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  padding: 10px 20px;
  font-size: 14px;
  font-weight: 500;
  border: none;
  border-radius: 8px;
  cursor: pointer;
  transition: all 0.2s;
  text-decoration: none;
}

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

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

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

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

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

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

.btn-sm {
  padding: 6px 12px;
  font-size: 12px;
}

.button-group {
  display: flex;
  gap: 12px;
  margin-top: 16px;
}

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

.student-card {
  background: var(--background-color);
  border-radius: 10px;
  padding: 16px;
  border: 1px solid var(--border-color);
  transition: all 0.2s;
}

.student-card:hover {
  border-color: var(--primary-color);
  box-shadow: var(--shadow);
}

.student-card h3 {
  font-size: 16px;
  margin-bottom: 8px;
}

.student-card p {
  font-size: 13px;
  color: var(--text-muted);
  margin-bottom: 4px;
}

.student-card .actions {
  display: flex;
  gap: 8px;
  margin-top: 12px;
}

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

table {
  width: 100%;
  border-collapse: collapse;
  font-size: 14px;
}

th, td {
  padding: 12px;
  text-align: left;
  border-bottom: 1px solid var(--border-color);
}

th {
  font-weight: 600;
  background-color: var(--background-color);
  color: var(--text-muted);
  text-transform: uppercase;
  font-size: 12px;
}

tr:hover {
  background-color: var(--background-color);
}

/* Tabs */
.tabs {
  display: flex;
  gap: 4px;
  background: var(--card-background);
  padding: 8px;
  border-radius: 12px;
  box-shadow: var(--shadow);
  margin-bottom: 24px;
}

.tab-btn {
  padding: 10px 20px;
  border: none;
  background: transparent;
  color: var(--text-muted);
  font-weight: 500;
  cursor: pointer;
  border-radius: 8px;
  transition: all 0.2s;
}

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

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

.tab-content {
  display: none;
}

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

/* Stats */
.stats-grid {
  display: grid;
  grid-template-columns: repeat(4, 1fr);
  gap: 16px;
}

.stat-item {
  text-align: center;
  padding: 16px;
  background: var(--background-color);
  border-radius: 10px;
}

.stat-value {
  display: block;
  font-size: 32px;
  font-weight: 700;
  color: var(--primary-color);
}

.stat-label {
  font-size: 13px;
  color: var(--text-muted);
}

/* Modal */
.modal {
  position: fixed;
  top: 0;
  left: 0;
  width: 100%;
  height: 100%;
  background: rgba(0,0,0,0.5);
  display: flex;
  align-items: center;
  justify-content: center;
  z-index: 1000;
}

.modal.hidden {
  display: none;
}

.modal-content {
  background: var(--card-background);
  border-radius: 16px;
  padding: 32px;
  max-width: 500px;
  width: 90%;
  max-height: 90vh;
  overflow-y: auto;
  position: relative;
}

.modal-content.modal-large {
  max-width: 900px;
}

.modal-content h2 {
  margin-bottom: 20px;
}

.close {
  position: absolute;
  top: 16px;
  right: 20px;
  font-size: 28px;
  cursor: pointer;
  color: var(--text-muted);
}

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

/* Semesters */
.semesters-container {
  margin-top: 24px;
}

.semester-block {
  background: var(--background-color);
  border-radius: 10px;
  padding: 16px;
  margin-bottom: 16px;
  border: 1px solid var(--border-color);
}

.semester-block h4 {
  font-size: 14px;
  color: var(--primary-color);
  margin-bottom: 12px;
  display: flex;
  justify-content: space-between;
  align-items: center;
}

.semester-block .gpa-summary {
  font-size: 12px;
  color: var(--text-muted);
  background: white;
  padding: 8px 12px;
  border-radius: 6px;
  margin-top: 12px;
}

/* Result Box */
.result-box {
  margin-top: 16px;
  padding: 16px;
  border-radius: 8px;
  font-size: 14px;
}

.result-box.success {
  background: #dcfce7;
  color: #166534;
  border: 1px solid #86efac;
}

.result-box.error {
  background: #fee2e2;
  color: #991b1b;
  border: 1px solid #fca5a5;
}

.hidden {
  display: none;
}

/* Loading */
.loading {
  text-align: center;
  color: var(--text-muted);
  padding: 40px;
}

/* Footer */
footer {
  text-align: center;
  padding: 30px 0;
  color: var(--text-muted);
  font-size: 14px;
}

/* Responsive */
@media (max-width: 768px) {
  header {
    flex-direction: column;
    gap: 16px;
  }

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

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

  .tabs {
    flex-wrap: wrap;
  }
}