:root {
  --primary: #2563eb;
  --primary-dark: #1d4ed8;
  --secondary: #64748b;
  --success: #22c55e;
  --warning: #f59e0b;
  --danger: #ef4444;
  --bg: #f1f5f9;
  --sidebar-bg: #0f172a;
  --sidebar-text: #94a3b8;
  --sidebar-active: #2563eb;
  --card-bg: #ffffff;
  --text: #1e293b;
  --text-light: #64748b;
  --border: #e2e8f0;
  --radius: 8px;
}

* { margin: 0; padding: 0; box-sizing: border-box; }
body { font-family: 'Segoe UI', Tahoma, sans-serif; background: var(--bg); color: var(--text); }

/* LOGIN */
#loginPage { display: flex; align-items: center; justify-content: center; min-height: 100vh; background: linear-gradient(135deg, #0f172a, #2563eb); }
.login-box { background: #fff; padding: 40px; border-radius: 12px; width: 400px; max-width: 90vw; box-shadow: 0 25px 50px rgba(0,0,0,0.25); }
.login-box h1 { text-align: center; color: var(--primary); margin-bottom: 8px; font-size: 28px; }
.login-box .subtitle { text-align: center; color: var(--text-light); margin-bottom: 30px; font-size: 14px; }
.form-group { margin-bottom: 18px; }
.form-group label { display: block; margin-bottom: 6px; font-weight: 600; font-size: 14px; }
.form-group input, .form-group select, .form-group textarea { width: 100%; padding: 10px 14px; border: 1px solid var(--border); border-radius: var(--radius); font-size: 14px; }
.form-group input:focus, .form-group select:focus, .form-group textarea:focus { outline: none; border-color: var(--primary); }
.btn { padding: 10px 20px; border: none; border-radius: var(--radius); cursor: pointer; font-size: 14px; font-weight: 600; transition: all 0.2s; display: inline-flex; align-items: center; gap: 6px; }
.btn-primary { background: var(--primary); color: #fff; }
.btn-primary:hover { background: var(--primary-dark); }
.btn-success { background: var(--success); color: #fff; }
.btn-danger { background: var(--danger); color: #fff; }
.btn-warning { background: var(--warning); color: #fff; }
.btn-secondary { background: var(--secondary); color: #fff; }
.btn-sm { padding: 6px 14px; font-size: 13px; }
.login-error { color: var(--danger); font-size: 13px; margin-top: 8px; display: none; text-align: center; }

/* APP LAYOUT */
#appPage { display: none; }
.sidebar { position: fixed; left: 0; top: 0; width: 260px; height: 100vh; background: var(--sidebar-bg); overflow-y: auto; z-index: 100; }
.sidebar-header { padding: 20px; border-bottom: 1px solid #1e293b; }
.sidebar-header h2 { color: #fff; font-size: 20px; }
.sidebar-header .inst-name { color: var(--sidebar-text); font-size: 12px; margin-top: 4px; }
.nav-section { padding: 12px 0; }
.nav-section-title { color: #475569; font-size: 11px; text-transform: uppercase; letter-spacing: 1px; padding: 4px 20px; margin-top: 4px; }
.nav-item { display: flex; align-items: center; padding: 10px 20px; color: var(--sidebar-text); cursor: pointer; transition: all 0.2s; font-size: 14px; }
.nav-item:hover, .nav-item.active { background: #1e293b; color: #fff; }
.nav-item.active { border-left: 3px solid var(--sidebar-active); }
.nav-item .icon { width: 20px; margin-right: 12px; text-align: center; }
.main-content { margin-left: 260px; min-height: 100vh; }
.topbar { background: #fff; padding: 14px 28px; display: flex; justify-content: space-between; align-items: center; border-bottom: 1px solid var(--border); position: sticky; top: 0; z-index: 50; }
.topbar .page-title { font-size: 20px; font-weight: 600; }
.topbar .user-info { display: flex; align-items: center; gap: 16px; }
.topbar .user-info span { font-size: 14px; color: var(--text-light); }
.page-content { padding: 24px 28px; }
.page { display: none; }
.page.active { display: block; }

/* CARDS */
.card { background: var(--card-bg); border-radius: var(--radius); padding: 20px; box-shadow: 0 1px 3px rgba(0,0,0,0.1); margin-bottom: 20px; }
.card-header { display: flex; justify-content: space-between; align-items: center; margin-bottom: 16px; }
.card-header h3 { font-size: 18px; }
.stats-grid { display: grid; grid-template-columns: repeat(auto-fit, minmax(220px, 1fr)); gap: 16px; margin-bottom: 24px; }
.stat-card { background: #fff; border-radius: var(--radius); padding: 20px; box-shadow: 0 1px 3px rgba(0,0,0,0.1); border-left: 4px solid var(--primary); }
.stat-card.success { border-left-color: var(--success); }
.stat-card.warning { border-left-color: var(--warning); }
.stat-card.danger { border-left-color: var(--danger); }
.stat-card .label { font-size: 13px; color: var(--text-light); margin-bottom: 4px; }
.stat-card .value { font-size: 28px; font-weight: 700; color: var(--text); }

/* TABLES */
.data-table { width: 100%; border-collapse: collapse; }
.data-table th, .data-table td { padding: 10px 14px; text-align: left; border-bottom: 1px solid var(--border); font-size: 14px; }
.data-table th { background: #f8fafc; font-weight: 600; color: var(--text-light); font-size: 13px; text-transform: uppercase; letter-spacing: 0.5px; }
.data-table tr:hover { background: #f8fafc; }
.badge { display: inline-block; padding: 3px 10px; border-radius: 12px; font-size: 12px; font-weight: 600; }
.badge-success { background: #dcfce7; color: #166534; }
.badge-warning { background: #fef3c7; color: #92400e; }
.badge-danger { background: #fee2e2; color: #991b1b; }
.badge-info { background: #dbeafe; color: #1e40af; }

/* FILTERS */
.filters { display: flex; gap: 12px; flex-wrap: wrap; margin-bottom: 16px; align-items: center; }
.filters select, .filters input { padding: 8px 12px; border: 1px solid var(--border); border-radius: var(--radius); font-size: 13px; }

/* MODAL */
.modal-overlay { display: none; position: fixed; inset: 0; background: rgba(0,0,0,0.5); z-index: 200; align-items: center; justify-content: center; }
.modal-overlay.active { display: flex; }
.modal { background: #fff; border-radius: 12px; width: 550px; max-width: 90vw; max-height: 85vh; overflow-y: auto; box-shadow: 0 25px 50px rgba(0,0,0,0.25); }
.modal-header { display: flex; justify-content: space-between; align-items: center; padding: 20px 24px; border-bottom: 1px solid var(--border); }
.modal-header h3 { font-size: 18px; }
.modal-close { background: none; border: none; font-size: 24px; cursor: pointer; color: var(--text-light); }
.modal-body { padding: 24px; }
.modal-footer { display: flex; justify-content: flex-end; gap: 10px; padding: 16px 24px; border-top: 1px solid var(--border); }

/* UTILITY */
.loading { text-align: center; padding: 40px; color: var(--text-light); }
.empty-state { text-align: center; padding: 60px 20px; color: var(--text-light); }
.text-right { text-align: right; }
.mb-16 { margin-bottom: 16px; }
.mt-16 { margin-top: 16px; }
.grid-2 { display: grid; grid-template-columns: 1fr 1fr; gap: 16px; }
.grid-3 { display: grid; grid-template-columns: repeat(3, 1fr); gap: 16px; }