:root {
  --blue-50: #eff6ff;
  --blue-100: #dbeafe;
  --blue-500: #3b82f6;
  --blue-600: #2563eb;
  --blue-700: #1d4ed8;
  --ink-900: #0f172a;
  --ink-700: #334155;
  --ink-500: #64748b;
  --ink-300: #cbd5e1;
  --ink-100: #f1f5f9;
  --surface: #ffffff;
  --bg: #f8fafc;
  --danger: #dc2626;
  --success: #16a34a;
  --radius-lg: 16px;
  --radius-md: 10px;
  --radius-sm: 6px;
  --shadow-sm: 0 1px 2px rgba(15, 23, 42, 0.06);
  --shadow-md: 0 4px 16px rgba(15, 23, 42, 0.08);
  --shadow-lg: 0 12px 32px rgba(15, 23, 42, 0.14);
  --transition: 160ms ease;
  color-scheme: light;
}

[data-theme="dark"] {
  --surface: #111827;
  --bg: #0b0f1a;
  --ink-900: #f1f5f9;
  --ink-700: #cbd5e1;
  --ink-500: #94a3b8;
  --ink-300: #334155;
  --ink-100: #1e293b;
  --blue-50: #0d1b34;
  color-scheme: dark;
}

* { box-sizing: border-box; }

html, body {
  margin: 0;
  padding: 0;
  background: var(--bg);
  color: var(--ink-900);
  font-family: "Segoe UI", -apple-system, BlinkMacSystemFont, "Helvetica Neue", Arial, sans-serif;
  transition: background var(--transition), color var(--transition);
}

.sr-only {
  position: absolute;
  width: 1px; height: 1px;
  padding: 0; margin: -1px;
  overflow: hidden;
  clip: rect(0,0,0,0);
  white-space: nowrap;
  border: 0;
}

button, input, select {
  font-family: inherit;
}

:focus-visible {
  outline: 3px solid var(--blue-500);
  outline-offset: 2px;
}

/* Header */
.app-header {
  background: var(--surface);
  border-bottom: 1px solid var(--ink-100);
  position: sticky;
  top: 0;
  z-index: 10;
}
.header-inner {
  max-width: 1100px;
  margin: 0 auto;
  padding: 18px 24px;
  display: flex;
  align-items: center;
  justify-content: space-between;
}
.brand { display: flex; align-items: center; gap: 14px; }
.brand-mark { font-size: 2rem; }
.brand h1 { font-size: 1.35rem; margin: 0; letter-spacing: -0.01em; }
.subtitle { margin: 2px 0 0; color: var(--ink-500); font-size: 0.9rem; }

.icon-btn {
  border: 1px solid var(--ink-100);
  background: var(--surface);
  color: var(--ink-700);
  width: 40px; height: 40px;
  border-radius: 50%;
  cursor: pointer;
  font-size: 1.05rem;
  display: flex; align-items: center; justify-content: center;
  transition: background var(--transition), transform var(--transition);
}
.icon-btn:hover { background: var(--ink-100); transform: rotate(20deg); }

main {
  max-width: 1100px;
  margin: 0 auto;
  padding: 28px 24px 80px;
  display: flex;
  flex-direction: column;
  gap: 24px;
}

.card {
  background: var(--surface);
  border-radius: var(--radius-lg);
  box-shadow: var(--shadow-sm);
  padding: 24px;
  border: 1px solid var(--ink-100);
}

.hidden { display: none !important; }

/* Upload */
.drop-zone {
  border: 2px dashed var(--ink-300);
  border-radius: var(--radius-lg);
  padding: 48px 24px;
  text-align: center;
  cursor: pointer;
  transition: border-color var(--transition), background var(--transition);
}
.drop-zone:hover, .drop-zone.dragover {
  border-color: var(--blue-500);
  background: var(--blue-50);
}
.drop-zone-icon { font-size: 2.2rem; color: var(--blue-600); }
.drop-zone-title { font-size: 1.1rem; font-weight: 600; margin: 8px 0 2px; }
.drop-zone-hint { color: var(--ink-500); margin: 0 0 16px; font-size: 0.9rem; }

.btn {
  border: none;
  border-radius: var(--radius-md);
  padding: 11px 20px;
  font-size: 0.95rem;
  font-weight: 600;
  cursor: pointer;
  transition: background var(--transition), transform var(--transition), opacity var(--transition);
}
.btn:disabled { opacity: 0.45; cursor: not-allowed; }
.btn-primary { background: var(--blue-600); color: #fff; }
.btn-primary:hover:not(:disabled) { background: var(--blue-700); }
.btn-secondary { background: var(--ink-100); color: var(--ink-900); }
.btn-secondary:hover:not(:disabled) { background: var(--ink-300); }
.btn-text { background: transparent; color: var(--ink-500); }
.btn-danger-outline { background: transparent; border: 1px solid var(--danger); color: var(--danger); }
.btn-danger-outline:hover { background: var(--danger); color: #fff; }
.btn-large { padding: 14px 28px; font-size: 1.05rem; }

.status-area { margin-top: 18px; color: var(--ink-500); font-size: 0.92rem; }
.upload-actions { display: flex; gap: 12px; margin-top: 18px; }

/* Loading overlay */
.loading-overlay {
  position: fixed;
  inset: 0;
  background: rgba(15, 23, 42, 0.55);
  display: flex;
  align-items: center;
  justify-content: center;
  z-index: 100;
}
.loading-panel {
  background: var(--surface);
  border-radius: var(--radius-lg);
  padding: 32px;
  width: min(360px, 90vw);
  text-align: center;
  box-shadow: var(--shadow-lg);
}
.spinner {
  width: 40px; height: 40px;
  border: 4px solid var(--ink-100);
  border-top-color: var(--blue-600);
  border-radius: 50%;
  margin: 0 auto 16px;
  animation: spin 0.8s linear infinite;
}
@keyframes spin { to { transform: rotate(360deg); } }
.progress-bar-track {
  background: var(--ink-100);
  border-radius: 999px;
  height: 10px;
  margin-top: 16px;
  overflow: hidden;
}
.progress-bar-fill {
  background: var(--blue-600);
  height: 100%;
  transition: width 120ms linear;
}
.progress-count { margin: 8px 0 20px; color: var(--ink-500); font-size: 0.9rem; }

@media (prefers-reduced-motion: reduce) {
  .spinner { animation-duration: 1.6s; }
  * { transition-duration: 0.01ms !important; animation-duration: 0.01ms !important; }
}

/* Dashboard */
.section-heading-row {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 16px;
  flex-wrap: wrap;
  margin-bottom: 16px;
}
.section-heading-row h2 { margin: 0; }
.search-input {
  border: 1px solid var(--ink-300);
  border-radius: var(--radius-md);
  padding: 9px 14px;
  font-size: 0.9rem;
  background: var(--surface);
  color: var(--ink-900);
  min-width: 220px;
}

.class-grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(220px, 1fr));
  gap: 16px;
}
.class-card {
  background: var(--surface);
  border: 1px solid var(--ink-100);
  border-radius: var(--radius-lg);
  padding: 20px;
  cursor: pointer;
  transition: transform var(--transition), box-shadow var(--transition);
  text-align: left;
}
.class-card:hover { transform: translateY(-2px); box-shadow: var(--shadow-md); }
.class-card h3 { margin: 0 0 6px; font-size: 1.05rem; }
.class-count { color: var(--blue-600); font-weight: 700; font-size: 1.4rem; }
.class-count-label { color: var(--ink-500); font-size: 0.85rem; }
.class-card .missing-badge {
  display: inline-block;
  margin-top: 8px;
  background: #fef3c7;
  color: #92400e;
  border-radius: 999px;
  padding: 2px 10px;
  font-size: 0.78rem;
  font-weight: 600;
}

/* Recent exports */
.recent-exports-list { list-style: none; padding: 0; margin: 0; display: flex; flex-direction: column; gap: 10px; }
.recent-exports-list li { display: flex; align-items: center; gap: 10px; color: var(--ink-700); font-size: 0.92rem; }
.recent-exports-list li::before { content: "✓"; color: var(--success); font-weight: 700; }

/* Export screen */
.export-screen { text-align: center; padding: 48px 24px; }
.export-icon { font-size: 2.6rem; }
.export-summary { font-size: 1.1rem; font-weight: 600; margin: 6px 0 2px; }
.export-sub { color: var(--ink-500); margin: 0 0 24px; }

/* Side panels */
.side-panel {
  position: fixed;
  top: 0; right: 0; bottom: 0;
  width: min(400px, 92vw);
  background: var(--surface);
  box-shadow: var(--shadow-lg);
  z-index: 90;
  display: flex;
  flex-direction: column;
  animation: slideIn 200ms ease;
}
@keyframes slideIn { from { transform: translateX(100%); } to { transform: translateX(0); } }
.side-panel-header {
  display: flex; align-items: center; justify-content: space-between;
  padding: 18px 20px;
  border-bottom: 1px solid var(--ink-100);
}
.side-panel-header h2 { margin: 0; font-size: 1.1rem; }
.side-panel-body { padding: 18px 20px; overflow-y: auto; flex: 1; display: flex; flex-direction: column; gap: 12px; }

.sort-row { display: flex; align-items: center; gap: 8px; font-size: 0.88rem; color: var(--ink-500); }
.sort-row select { border: 1px solid var(--ink-300); border-radius: var(--radius-sm); padding: 6px 8px; background: var(--surface); color: var(--ink-900); }

.preview-list { list-style: none; padding: 0; margin: 0; display: flex; flex-direction: column; gap: 4px; }
.preview-list li {
  padding: 10px 12px;
  border-radius: var(--radius-sm);
  display: flex;
  justify-content: space-between;
  font-size: 0.92rem;
}
.preview-list li:hover { background: var(--ink-100); }
.preview-list .student-meta { color: var(--ink-500); font-size: 0.82rem; }

.duplicate-list { display: flex; flex-direction: column; gap: 16px; }
.duplicate-group {
  border: 1px solid var(--ink-100);
  border-radius: var(--radius-md);
  padding: 14px;
}
.duplicate-group h4 { margin: 0 0 4px; font-size: 0.98rem; }
.duplicate-group .dup-ref { color: var(--ink-500); font-size: 0.82rem; margin-bottom: 10px; }
.dup-option { display: flex; align-items: flex-start; gap: 8px; padding: 6px 0; font-size: 0.88rem; }
.dup-option .dup-file-meta { color: var(--ink-500); font-size: 0.8rem; }
.dup-quick-actions { display: flex; gap: 8px; margin-top: 8px; flex-wrap: wrap; }
.dup-quick-actions button {
  font-size: 0.8rem;
  padding: 6px 10px;
  border-radius: 999px;
  border: 1px solid var(--ink-300);
  background: transparent;
  color: var(--ink-700);
  cursor: pointer;
}
.dup-quick-actions button:hover { background: var(--ink-100); }

/* Modal */
.modal-backdrop {
  position: fixed; inset: 0;
  background: rgba(15,23,42,0.5);
  display: flex; align-items: center; justify-content: center;
  z-index: 110;
}
.modal {
  background: var(--surface);
  border-radius: var(--radius-lg);
  padding: 28px;
  width: min(420px, 90vw);
  box-shadow: var(--shadow-lg);
}
.modal h2 { margin-top: 0; }
.modal-actions { display: flex; gap: 10px; margin-top: 20px; flex-wrap: wrap; }

/* Settings */
.settings-body label { font-size: 0.85rem; font-weight: 600; color: var(--ink-700); margin-top: 6px; }
.settings-body input, .settings-body select {
  border: 1px solid var(--ink-300);
  border-radius: var(--radius-sm);
  padding: 9px 10px;
  background: var(--surface);
  color: var(--ink-900);
  font-size: 0.9rem;
}
.settings-body h3 { margin: 16px 0 4px; font-size: 0.95rem; }
.hint-text { color: var(--ink-500); font-size: 0.8rem; margin: 0 0 8px; }
.class-size-inputs { display: flex; flex-direction: column; gap: 8px; }
.class-size-row { display: flex; align-items: center; justify-content: space-between; gap: 10px; }
.class-size-row span { font-size: 0.88rem; }
.class-size-row input { width: 80px; }

/* Toasts */
.toast-container {
  position: fixed;
  bottom: 20px; left: 50%;
  transform: translateX(-50%);
  display: flex; flex-direction: column; gap: 8px;
  z-index: 200;
}
.toast {
  background: var(--ink-900);
  color: #fff;
  padding: 12px 18px;
  border-radius: var(--radius-md);
  font-size: 0.9rem;
  box-shadow: var(--shadow-md);
  animation: fadeUp 200ms ease;
}
.toast.toast-error { background: var(--danger); }
.toast.toast-success { background: var(--success); }
@keyframes fadeUp { from { opacity: 0; transform: translateY(8px); } to { opacity: 1; transform: translateY(0); } }

@media (max-width: 640px) {
  .header-inner { padding: 14px 16px; }
  main { padding: 20px 14px 60px; }
  .side-panel { width: 100vw; }
}