/* ===== CSS Variables ===== */
:root {
  --primary: #2B6CB0;
  --primary-light: #3182CE;
  --primary-bg: #EBF4FF;
  --sidebar-bg: #1A365D;
  --sidebar-hover: #2A4A7F;
  --success: #38A169;
  --warning: #D69E2E;
  --danger: #E53E3E;
  --page-bg: #F7FAFC;
  --card-bg: #FFFFFF;
  --border: #E2E8F0;
  --text: #2D3748;
  --text-secondary: #718096;
  --radius: 6px;
  --shadow: 0 1px 3px rgba(0,0,0,0.08), 0 1px 2px rgba(0,0,0,0.06);
  --shadow-md: 0 4px 6px rgba(0,0,0,0.07), 0 2px 4px rgba(0,0,0,0.06);
  --sidebar-width: 240px;
  --topbar-height: 56px;
  --font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, 'Helvetica Neue', sans-serif;
  --transition: 150ms ease;
}

/* ===== Reset ===== */
*, *::before, *::after { margin:0; padding:0; box-sizing:border-box; }
html { font-size:14px; }
body { font-family:var(--font-family); color:var(--text); background:var(--page-bg); line-height:1.6; }
a { color:var(--primary-light); text-decoration:none; }
a:hover { color:var(--primary); }
img { max-width:100%; }
table { border-collapse:collapse; width:100%; }
input,select,textarea,button { font-family:inherit; font-size:inherit; }
.hidden { display:none !important; }

/* ===== Login Page ===== */
.login-page {
  min-height:100vh; display:flex; align-items:center; justify-content:center;
  background:linear-gradient(135deg, #1A365D 0%, #2B6CB0 100%);
}
.login-card {
  background:var(--card-bg); border-radius:8px; padding:40px 36px; width:380px;
  box-shadow:0 20px 60px rgba(0,0,0,0.2);
}
.login-logo { text-align:center; margin-bottom:16px; }
.login-title { text-align:center; font-size:20px; font-weight:600; color:var(--text); margin-bottom:4px; }
.login-subtitle { text-align:center; font-size:13px; color:var(--text-secondary); margin-bottom:28px; }

/* ===== Main App Layout ===== */
.main-app { display:flex; min-height:100vh; }

/* ===== Sidebar ===== */
.sidebar {
  width:var(--sidebar-width); background:var(--sidebar-bg); color:#fff;
  display:flex; flex-direction:column; position:fixed; top:0; left:0; bottom:0; z-index:100;
}
.sidebar-logo {
  display:flex; align-items:center; gap:10px; padding:16px 20px;
  border-bottom:1px solid rgba(255,255,255,0.1); font-size:16px; font-weight:600;
}
.sidebar-nav { flex:1; padding:12px 0; overflow-y:auto; }
.nav-item {
  display:flex; align-items:center; gap:10px; padding:10px 20px; color:rgba(255,255,255,0.7);
  transition:background var(--transition), color var(--transition); cursor:pointer; font-size:14px;
}
.nav-item:hover { background:var(--sidebar-hover); color:#fff; }
.nav-item.active { background:var(--primary); color:#fff; }
.nav-item svg { flex-shrink:0; }
.sidebar-footer {
  padding:12px 20px; border-top:1px solid rgba(255,255,255,0.1);
  font-size:12px; color:rgba(255,255,255,0.4);
}

/* ===== Main Content ===== */
.main-content {
  flex:1; margin-left:var(--sidebar-width); display:flex; flex-direction:column; min-height:100vh;
}

/* ===== Topbar ===== */
.topbar {
  height:var(--topbar-height); background:var(--card-bg); display:flex;
  align-items:center; justify-content:space-between; padding:0 24px;
  border-bottom:1px solid var(--border); box-shadow:0 1px 2px rgba(0,0,0,0.04);
  position:sticky; top:0; z-index:50;
}
.topbar h2 { font-size:16px; font-weight:600; }
.topbar-right { display:flex; align-items:center; gap:12px; }
.topbar-user { font-size:13px; color:var(--text-secondary); }

/* ===== Page Content ===== */
.page-content { padding:24px; flex:1; }

/* ===== Stat Cards ===== */
.stat-cards { display:grid; grid-template-columns:repeat(4,1fr); gap:20px; margin-bottom:24px; }
.stat-card {
  background:var(--card-bg); border-radius:var(--radius); padding:20px;
  display:flex; align-items:center; gap:16px; box-shadow:var(--shadow);
}
.stat-icon {
  width:52px; height:52px; border-radius:var(--radius); display:flex;
  align-items:center; justify-content:center; flex-shrink:0;
}
.stat-value { font-size:28px; font-weight:700; line-height:1.2; }
.stat-label { font-size:13px; color:var(--text-secondary); margin-top:2px; }

/* ===== Cards ===== */
.card {
  background:var(--card-bg); border-radius:var(--radius); box-shadow:var(--shadow);
}
.card-header {
  display:flex; align-items:center; justify-content:space-between;
  padding:16px 20px; border-bottom:1px solid var(--border);
}
.card-header h3 { font-size:15px; font-weight:600; }
.card-hint { font-size:12px; color:var(--text-secondary); }
.card-body { padding:16px 20px; }

/* ===== Chart Row ===== */
.chart-row { display:grid; grid-template-columns:1.5fr 1fr; gap:20px; margin-bottom:24px; }
.chart-card canvas { width:100% !important; max-width:100%; }
.chart-card-scroll { max-height:420px; display:flex; flex-direction:column; }
.chart-card-scroll .card-header { flex-shrink:0; }
.chart-scroll-body { overflow-y:auto; flex:1; padding:8px 20px 16px; }
.chart-scroll-body canvas { min-height:200px; }

/* ===== Data Table ===== */
.data-table { width:100%; }
.data-table thead th {
  background:#F7FAFC; padding:10px 12px; text-align:left; font-size:13px;
  font-weight:600; color:var(--text-secondary); border-bottom:2px solid var(--border);
  white-space:nowrap;
}
.data-table tbody td {
  padding:10px 12px; border-bottom:1px solid var(--border); font-size:13px;
  vertical-align:middle;
}
.data-table tbody tr:hover { background:#F7FAFC; }
.data-table tbody tr:nth-child(even) { background:#FAFCFE; }
.data-table tbody tr:nth-child(even):hover { background:#F0F5FA; }

/* ===== Buttons ===== */
.btn {
  display:inline-flex; align-items:center; justify-content:center; gap:6px;
  padding:8px 16px; border:1px solid transparent; border-radius:var(--radius);
  font-size:13px; font-weight:500; cursor:pointer; transition:all var(--transition);
  white-space:nowrap; line-height:1.4;
}
.btn:hover { opacity:0.85; }
.btn:active { transform:scale(0.98); }
.btn-primary { background:var(--primary); color:#fff; border-color:var(--primary); }
.btn-primary:hover { background:var(--primary-light); }
.btn-success { background:var(--success); color:#fff; border-color:var(--success); }
.btn-danger { background:var(--danger); color:#fff; border-color:var(--danger); }
.btn-warning { background:var(--warning); color:#fff; border-color:var(--warning); }
.btn-outline { background:transparent; color:var(--text); border-color:var(--border); }
.btn-outline:hover { border-color:var(--primary); color:var(--primary); }
.btn-sm { padding:5px 10px; font-size:12px; }
.btn-block { width:100%; }
.btn[disabled] { opacity:0.5; cursor:not-allowed; }

/* ===== Page Toolbar ===== */
.page-toolbar {
  display:flex; align-items:center; justify-content:space-between;
  margin-bottom:16px; gap:12px; flex-wrap:wrap;
}
.toolbar-left { display:flex; align-items:center; gap:10px; flex-wrap:wrap; }
.toolbar-right { display:flex; align-items:center; gap:10px; }

/* ===== Forms ===== */
.form-group { margin-bottom:16px; }
.form-group label { display:block; font-size:13px; font-weight:500; margin-bottom:5px; color:var(--text); }
.form-input, .form-select, .form-textarea {
  width:100%; padding:8px 12px; border:1px solid var(--border); border-radius:var(--radius);
  font-size:13px; color:var(--text); background:var(--card-bg);
  transition:border-color var(--transition);
}
.form-input:focus, .form-select:focus, .form-textarea:focus {
  outline:none; border-color:var(--primary); box-shadow:0 0 0 3px rgba(43,108,176,0.1);
}
.form-textarea { resize:vertical; min-height:80px; }
.form-select { cursor:pointer; }
.form-row { display:flex; align-items:center; gap:12px; margin-bottom:12px; }
.form-label { font-size:13px; font-weight:500; min-width:fit-content; white-space:nowrap; }
.form-hint { font-size:12px; color:var(--text-secondary); margin-top:4px; }
.form-inline { display:flex; gap:12px; }
.form-inline .form-group { flex:1; }

/* ===== Status Tags ===== */
.tag {
  display:inline-block; padding:2px 8px; border-radius:3px; font-size:12px; font-weight:500;
}
.tag-success { background:#F0FFF4; color:var(--success); }
.tag-warning { background:#FFFFF0; color:var(--warning); }
.tag-danger { background:#FFF5F5; color:var(--danger); }
.tag-info { background:var(--primary-bg); color:var(--primary); }
.tag-default { background:#EDF2F7; color:var(--text-secondary); }

/* ===== Modal ===== */
.modal-overlay {
  position:fixed; inset:0; background:rgba(0,0,0,0.45); z-index:1000;
  display:flex; align-items:center; justify-content:center;
  animation:fadeIn 150ms ease;
}
.modal {
  background:var(--card-bg); border-radius:8px; width:600px; max-width:90vw;
  max-height:85vh; display:flex; flex-direction:column;
  animation:scaleIn 150ms ease-out;
}
.modal-header {
  display:flex; align-items:center; justify-content:space-between;
  padding:16px 20px; border-bottom:1px solid var(--border);
}
.modal-header h3 { font-size:16px; font-weight:600; }
.modal-close {
  width:28px; height:28px; border:none; background:none; font-size:20px;
  cursor:pointer; color:var(--text-secondary); border-radius:var(--radius);
  display:flex; align-items:center; justify-content:center;
}
.modal-close:hover { background:#EDF2F7; color:var(--text); }
.modal-body { padding:20px; overflow-y:auto; flex:1; }
.modal-footer {
  display:flex; align-items:center; justify-content:flex-end; gap:10px;
  padding:12px 20px; border-top:1px solid var(--border);
}
.modal.wide { width:800px; }

/* ===== Toast ===== */
.toast-container {
  position:fixed; top:20px; right:20px; z-index:2000;
  display:flex; flex-direction:column; gap:8px;
}
.toast {
  padding:12px 20px; border-radius:var(--radius); font-size:13px;
  box-shadow:var(--shadow-md); min-width:240px; max-width:400px;
  animation:slideInRight 200ms ease-out;
  display:flex; align-items:center; gap:8px;
}
.toast-success { background:#F0FFF4; color:var(--success); border-left:3px solid var(--success); }
.toast-error { background:#FFF5F5; color:var(--danger); border-left:3px solid var(--danger); }
.toast-info { background:var(--primary-bg); color:var(--primary); border-left:3px solid var(--primary); }
.toast-warning { background:#FFFFF0; color:var(--warning); border-left:3px solid var(--warning); }

/* ===== Pagination ===== */
.pagination {
  display:flex; align-items:center; justify-content:flex-end; gap:4px;
  padding:12px 0; font-size:13px;
}
.pagination button {
  min-width:32px; height:32px; border:1px solid var(--border); border-radius:var(--radius);
  background:var(--card-bg); cursor:pointer; font-size:13px; transition:all var(--transition);
}
.pagination button:hover { border-color:var(--primary); color:var(--primary); }
.pagination button.active { background:var(--primary); color:#fff; border-color:var(--primary); }
.pagination button:disabled { opacity:0.4; cursor:not-allowed; }
.pagination .page-info { color:var(--text-secondary); margin:0 8px; }

/* ===== Drag ===== */
.drag-handle { cursor:grab; color:var(--text-secondary); user-select:none; }
.drag-handle:active { cursor:grabbing; }
.drag-over { background:var(--primary-bg) !important; }
.dragging { opacity:0.5; }

/* ===== Tab Editor (课程介绍) ===== */
.tab-editor {}
.tab-nav { display:flex; border-bottom:2px solid var(--border); margin-bottom:12px; }
.tab-nav-item {
  padding:8px 16px; cursor:pointer; font-size:13px; font-weight:500;
  color:var(--text-secondary); border-bottom:2px solid transparent; margin-bottom:-2px;
  transition:all var(--transition);
}
.tab-nav-item:hover { color:var(--primary); }
.tab-nav-item.active { color:var(--primary); border-bottom-color:var(--primary); }
.tab-pane { display:none; }
.tab-pane.active { display:block; }

/* ===== Image Upload ===== */
.upload-area {
  width:120px; height:120px; border:2px dashed var(--border); border-radius:var(--radius);
  display:flex; flex-direction:column; align-items:center; justify-content:center;
  cursor:pointer; color:var(--text-secondary); font-size:12px; transition:border-color var(--transition);
  position:relative; overflow:hidden;
}
.upload-area:hover { border-color:var(--primary); color:var(--primary); }
.upload-area img { position:absolute; inset:0; width:100%; height:100%; object-fit:cover; }
.upload-area .upload-icon { font-size:24px; margin-bottom:4px; }

/* ===== Confirm Dialog ===== */
.confirm-text { text-align:center; padding:20px 0; font-size:15px; color:var(--text); }

/* ===== Checkbox ===== */
.data-table input[type="checkbox"] {
  width:16px; height:16px; cursor:pointer; accent-color:var(--primary);
}

/* ===== Animations ===== */
@keyframes fadeIn { from { opacity:0; } to { opacity:1; } }
@keyframes scaleIn { from { opacity:0; transform:scale(0.95); } to { opacity:1; transform:scale(1); } }
@keyframes slideInRight { from { opacity:0; transform:translateX(30px); } to { opacity:1; transform:translateX(0); } }

/* ===== Login Form ===== */
.login-card .form-group { margin-bottom:18px; }
.login-card .form-group label { font-size:13px; font-weight:500; color:var(--text); margin-bottom:6px; }
.login-card .form-input {
  width:100%; padding:10px 14px; border:1px solid var(--border); border-radius:var(--radius);
  font-size:14px;
}
.login-card .form-input:focus {
  outline:none; border-color:var(--primary); box-shadow:0 0 0 3px rgba(43,108,176,0.15);
}
.login-card .btn-block { margin-top:8px; padding:10px; font-size:15px; }

/* ===== Scrollbar ===== */
::-webkit-scrollbar { width:6px; height:6px; }
::-webkit-scrollbar-thumb { background:#CBD5E0; border-radius:3px; }
::-webkit-scrollbar-thumb:hover { background:#A0AEC0; }
::-webkit-scrollbar-track { background:transparent; }

/* ===== Empty State ===== */
.empty-state { text-align:center; padding:48px 20px; color:var(--text-secondary); }
.empty-state svg { margin-bottom:12px; opacity:0.4; }
.empty-state p { font-size:14px; }

/* ===== Responsive (Desktop-first, 1024px+) ===== */
@media (max-width:1200px) {
  .stat-cards { grid-template-columns:repeat(2,1fr); }
  .chart-row { grid-template-columns:1fr; }
}
@media (max-width:768px) {
  .sidebar { transform:translateX(-100%); }
  .sidebar.open { transform:translateX(0); }
  .main-content { margin-left:0; }
  .stat-cards { grid-template-columns:1fr; }
}