:root {
    --primary: #2563eb;
    --secondary: #f97316;
    --success: #10b981;
    --danger: #ef4444;
    --gray: #f3f4f6;
    --text: #1f2937;
}
* {box-sizing:border-box;margin:0;padding:0;font-family:-apple-system,BlinkMacSystemFont,"Segoe UI",sans-serif;}
body {color:var(--text);background:#f9fafb;line-height:1.6;}
a {text-decoration:none;color:inherit;}
img {max-width:100%;}

.container {max-width:1200px;margin:0 auto;padding:0 1rem;}

/* Nút bấm */
.btn {display:inline-block;padding:.6rem 1.2rem;border:none;border-radius:8px;font-size:1rem;cursor:pointer;transition:all .2s;text-align:center;}
.btn-primary {background:var(--primary);color:white;}
.btn-primary:hover {background:#1d4ed8;}
.btn-secondary {background:var(--secondary);color:white;}
.btn-secondary:hover {background:#ea580c;}
.btn-success {background:var(--success);color:white;}
.btn-danger {background:var(--danger);color:white;}
.btn-outline {background:transparent;border:2px solid var(--primary);color:var(--primary);}

/* Form */
.form-group {margin-bottom:1rem;}
.form-group label {display:block;margin-bottom:.5rem;font-weight:500;}
.form-group input, .form-group select, .form-group textarea {width:100%;padding:.75rem;border:2px solid #e5e7eb;border-radius:8px;font-size:1rem;}
.form-group input:focus, .form-group select:focus, .form-group textarea:focus {outline:none;border-color:var(--primary);}

/* Thông báo */
.alert {padding:1rem 1.5rem;border-radius:8px;margin-bottom:1rem;}
.alert-success {background:#dcfce7;color:#166534;}
.alert-error {background:#fee2e2;color:#991b1b;}
.alert-info {background:#dbeafe;color:#1e40af;}
.text-center {text-align:center;}

/* Bảng */
table {width:100%;border-collapse:collapse;background:white;border-radius:8px;overflow:hidden;}
th, td {padding:.75rem 1rem;text-align:left;border-bottom:1px solid #eee;}
th {background:#f8fafc;font-weight:600;}
tr:hover {background:#f9fafb;}

/* Header & Menu */
header {background:white;box-shadow:0 2px 4px rgba(0,0,0,.05);position:sticky;top:0;z-index:100;}
.header-inner {max-width:1200px;margin:0 auto;padding:1rem;display:flex;justify-content:space-between;align-items:center;flex-wrap:wrap;gap:1rem;}
.logo {font-size:1.5rem;font-weight:bold;color:var(--primary);}

/* Navigation */
nav {display:flex;align-items:center;gap:1rem;flex-wrap:wrap;}
nav a {padding:.5rem .75rem;border-radius:6px;transition:background .2s;}
nav a:hover, nav a.active {background:var(--primary);color:white;}

/* Dropdown menu */
.dropdown {position:relative;display:inline-block;}
.dropdown-menu {display:none;position:absolute;top:100%;left:0;background:white;min-width:180px;box-shadow:0 4px 12px rgba(0,0,0,.1);border-radius:8px;z-index:1000;}
.dropdown:hover .dropdown-menu {display:block;}
.dropdown-menu a {display:block;padding:.6rem 1rem;white-space:nowrap;}
.dropdown-menu a:hover {background:#f3f4f6;}

/* Footer */
footer {background:#1f2937;color:white;padding:3rem 1rem 1rem;margin-top:4rem;}
.footer-inner {max-width:1200px;margin:0 auto;}
.footer-bottom {text-align:center;padding-top:2rem;border-top:1px solid #374151;margin-top:2rem;color:#9ca3af;font-size:.9rem;}

/* Responsive */
@media (max-width:768px) {
    .header-inner {justify-content:center;}
    nav {width:100%;justify-content:center;}
    h1 {font-size:1.8rem;}
}