:root {
  --fd-surface-muted: #f1f5f9;
  --fd-surface-soft: #eef2ff;
  --fd-info-bg: #e0f2fe;
  --fd-info-border: #38bdf8;
  --fd-success-bg: #dcfce7;
  --fd-success-border: #22c55e;
  --fd-danger-bg: #fee2e2;
  --fd-danger-border: #ef4444;
  --fd-hint-bg: #e2e8f0;
}

[data-theme="dark"] {
  --fd-surface-muted: #1f2937;
  --fd-surface-soft: #1e293b;
  --fd-info-bg: rgba(14, 116, 144, 0.28);
  --fd-info-border: #38bdf8;
  --fd-success-bg: rgba(22, 101, 52, 0.28);
  --fd-success-border: #22c55e;
  --fd-danger-bg: rgba(127, 29, 29, 0.32);
  --fd-danger-border: #f87171;
  --fd-hint-bg: #334155;
}

.site-header .logo {
  font-size: 2rem;
}

.site-header .tagline {
  max-width: 640px;
}

main {
  padding-top: 40px;
}

.welcome-section {
  text-align: center;
  margin-bottom: 24px;
  background: linear-gradient(135deg, var(--fd-surface-soft) 0%, var(--fd-surface-muted) 100%);
}

.welcome-section h2 {
  color: var(--text);
  font-size: 1.8rem;
  margin-bottom: 8px;
}

.welcome-section p {
  color: var(--muted);
  font-size: 1.05rem;
}

.students-info {
  background: var(--fd-success-bg);
  border: 2px solid var(--fd-success-border);
  border-radius: var(--radius);
  padding: 20px;
  margin-bottom: 24px;
  text-align: center;
  box-shadow: var(--shadow);
}

.card {
  border-radius: var(--radius);
}

.students-count {
  font-size: 2rem;
  font-weight: 700;
  color: var(--text);
}

.students-status {
  color: var(--muted);
  font-size: 0.95rem;
  margin-top: 4px;
}

.section-title {
  text-align: center;
}

.data-source-options {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(280px, 1fr));
  gap: 16px;
  margin-bottom: 24px;
}

.data-option {
  display: flex;
  align-items: center;
  padding: 20px;
  border: 2px solid var(--border);
  border-radius: var(--radius);
  cursor: pointer;
  transition: all var(--transition);
  background: var(--surface);
  position: relative;
}

.data-option:hover,
.data-option.active {
  border-color: var(--primary);
  box-shadow: var(--shadow);
}

.data-option:focus-within,
.toggle-option:focus-visible,
.sort-option:focus-visible {
  outline: 2px solid var(--primary);
  outline-offset: 2px;
}

.data-option.active {
  background: rgba(102, 126, 234, 0.08);
}

.data-option input[type="radio"] {
  position: absolute;
  right: 20px;
  top: 50%;
  transform: translateY(-50%);
  width: 20px;
  height: 20px;
  accent-color: var(--primary);
}

.option-icon {
  font-size: 1.9rem;
  margin-right: 14px;
}

.option-content h4 {
  color: var(--text);
  font-size: 1.05rem;
}

.option-content p {
  color: var(--muted);
  font-size: 0.9rem;
}

.input-section {
  background: var(--surface);
  border: 2px solid var(--border);
  border-radius: var(--radius);
  padding: 24px;
  margin-bottom: 24px;
  display: none;
  box-shadow: var(--shadow);
}

.input-section.active {
  display: block;
}

.input-section.manual {
  background: var(--fd-info-bg);
  border-color: var(--fd-info-border);
}

.input-section.csv {
  background: var(--fd-success-bg);
  border-color: var(--fd-success-border);
}

.section-header {
  text-align: center;
  margin-bottom: 16px;
}

.section-header h3 {
  color: var(--text);
  margin-bottom: 4px;
}

.section-header p {
  color: var(--muted);
}

textarea {
  width: 100%;
  min-height: 180px;
  padding: 16px;
  border: 2px solid var(--border);
  border-radius: 12px;
  font-family: inherit;
  font-size: 0.95rem;
  line-height: 1.6;
  resize: vertical;
  background: var(--surface);
  color: var(--text);
}

textarea:focus {
  outline: none;
  border-color: var(--primary);
  box-shadow: 0 0 0 3px rgba(102, 126, 234, 0.15);
}

.input-hints {
  margin-top: 12px;
  display: flex;
  gap: 8px;
  justify-content: center;
  flex-wrap: wrap;
}

.hint-item {
  background: var(--fd-hint-bg);
  padding: 6px 12px;
  border-radius: 999px;
  font-size: 0.8rem;
  color: var(--text);
}

.hint-item code {
  background: var(--surface);
  padding: 2px 6px;
  border-radius: 4px;
}

.file-upload-area {
  border: 2px dashed var(--border);
  border-radius: var(--radius);
  padding: 36px 20px;
  text-align: center;
  cursor: pointer;
  transition: all var(--transition);
  background: var(--surface);
  margin-bottom: 16px;
}

.file-upload-area:hover,
.file-upload-area.dragover {
  border-color: var(--success);
  background: var(--fd-success-bg);
}

.upload-icon {
  font-size: 2.5rem;
  margin-bottom: 10px;
}

.upload-text {
  font-size: 1rem;
  color: var(--text);
  margin-bottom: 6px;
}

.upload-hint {
  font-size: 0.85rem;
  color: var(--muted);
}

.configuration-section {
  display: none;
}

.config-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(250px, 1fr));
  gap: 24px;
}

.config-group h4 {
  color: var(--text);
  margin-bottom: 14px;
}

.toggle-group {
  display: flex;
  flex-direction: column;
  gap: 10px;
}

.toggle-option {
  display: flex;
  align-items: center;
  padding: 14px;
  border: 2px solid var(--border);
  border-radius: 10px;
  cursor: pointer;
  transition: all var(--transition);
  background: var(--surface);
}

.toggle-option:hover,
.toggle-option.active {
  border-color: var(--primary);
}

.toggle-option.active {
  background: rgba(102, 126, 234, 0.08);
}

.toggle-icon {
  font-size: 1.2rem;
  margin-right: 10px;
}

.toggle-content span {
  display: block;
  color: var(--text);
  font-weight: 600;
}

.toggle-content small {
  color: var(--muted);
}

.number-input-container {
  display: flex;
  align-items: center;
  gap: 10px;
  background: var(--fd-surface-muted);
  padding: 12px;
  border-radius: 10px;
  margin-top: 14px;
}

.number-input-container input {
  flex: 1;
  padding: 10px;
  border: 2px solid var(--border);
  border-radius: 8px;
  text-align: center;
  font-size: 1rem;
  font-weight: 600;
  background: var(--surface);
  color: var(--text);
}

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

.number-input-container label {
  color: var(--text);
  font-weight: 600;
}

.sort-options {
  display: flex;
  gap: 10px;
  flex-wrap: wrap;
}

.sort-option {
  display: flex;
  align-items: center;
  gap: 6px;
  padding: 10px 16px;
  border: 2px solid var(--border);
  border-radius: 999px;
  cursor: pointer;
  transition: all var(--transition);
  background: var(--surface);
  color: var(--text);
  font-size: 0.9rem;
}

.sort-option:hover {
  border-color: var(--primary);
}

.sort-option.active {
  border-color: var(--primary);
  background: linear-gradient(135deg, var(--primary), var(--primary-dark));
  color: #fff;
}

.action-buttons {
  display: flex;
  gap: 12px;
  justify-content: center;
  margin-top: 20px;
  flex-wrap: wrap;
}

#actionSection {
  margin-bottom: 24px;
}

.action-buttons .btn {
  min-height: 44px;
}

.btn-large {
  padding: 16px 32px;
  font-size: 1.05rem;
}

.results {
  margin-bottom: 24px;
}

.results-header {
  text-align: center;
  margin-bottom: 20px;
}

.results-header h2 {
  color: var(--text);
  margin-bottom: 4px;
}

.results-header p {
  color: var(--muted);
}

.groups-container {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(260px, 1fr));
  gap: 16px;
}

.group {
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  overflow: hidden;
  box-shadow: var(--shadow);
  transition: all var(--transition);
}

.group:hover {
  transform: translateY(-3px);
  box-shadow: var(--shadow-hover);
}

.group-header h4,
.results-header h2 {
  letter-spacing: -0.2px;
}

.group-header {
  background: linear-gradient(135deg, var(--primary), var(--primary-dark));
  color: #fff;
  padding: 14px;
  text-align: center;
}

.group-header h4 {
  margin-bottom: 2px;
}

.group-size {
  font-size: 0.85rem;
  opacity: 0.9;
}

.student-list {
  list-style: none;
}

.student-item {
  padding: 12px 14px;
  border-bottom: 1px solid var(--border);
  display: flex;
  justify-content: space-between;
  align-items: center;
}

.student-item:last-child {
  border-bottom: 0;
}

.student-name {
  font-weight: 600;
  color: var(--text);
}

.student-id {
  color: var(--muted);
  font-size: 0.85rem;
}

.alert-error {
  background: var(--fd-danger-bg);
  border-color: var(--fd-danger-border);
  color: var(--text);
}

.alert-success {
  background: var(--fd-success-bg);
  border-color: var(--fd-success-border);
  color: var(--text);
}

.suspense-container {
  text-align: center;
  padding: 44px 20px;
  background: linear-gradient(135deg, var(--primary), var(--primary-dark));
  border-radius: var(--radius);
  color: #fff;
}

.suspense-spinner {
  width: 50px;
  height: 50px;
  border: 4px solid rgba(255, 255, 255, 0.3);
  border-top: 4px solid #fff;
  border-radius: 50%;
  animation: spin 1s linear infinite;
  margin: 0 auto 16px;
}

.suspense-message {
  font-size: 1.2rem;
  animation: pulse 2s infinite;
}

@keyframes spin {
  0% { transform: rotate(0deg); }
  100% { transform: rotate(360deg); }
}

@keyframes pulse {
  0%, 100% { opacity: 1; }
  50% { opacity: 0.65; }
}

@media (max-width: 768px) {
  .site-header .logo {
    font-size: 1.65rem;
  }

  .welcome-section h2 {
    font-size: 1.35rem;
  }

  .data-option {
    flex-direction: column;
    text-align: center;
    padding: 16px;
  }

  .data-option input[type="radio"] {
    position: static;
    transform: none;
    margin-top: 8px;
  }

  .option-icon {
    margin-right: 0;
    margin-bottom: 8px;
  }

  .config-grid,
  .groups-container {
    grid-template-columns: 1fr;
  }

  .action-buttons {
    flex-direction: column;
  }

  .action-buttons .btn {
    width: 100%;
  }
}