:root {
    --primary: #2563eb; --primary-dark: #1e40af; --success: #10b981; --danger: #ef4444;
    --bg-main: #f8fafc; --sidebar-bg: #1e293b; --text-main: #334155; --white: #ffffff;
    --border: #e2e8f0; --radius: 8px; --shadow: 0 4px 6px -1px rgb(0 0 0 / 0.1);
}
* { box-sizing: border-box; margin: 0; padding: 0; }
body { font-family: 'Inter', sans-serif; background: var(--bg-main); color: var(--text-main); display: flex; min-height: 100vh; }
.sidebar { width: 260px; background: var(--sidebar-bg); color: var(--white); position: fixed; height: 100vh; display: flex; flex-direction: column; }
.sidebar-header { padding: 2rem; border-bottom: 1px solid #334155; }
.sidebar-header h2 { color: var(--primary); }
.sidebar-nav a { display: block; padding: 0.75rem 2rem; color: #cbd5e1; text-decoration: none; }
.sidebar-nav a:hover, .sidebar-nav a.active { background: #334155; color: var(--white); border-left: 4px solid var(--primary); }
.main-content { flex: 1; margin-left: 260px; padding: 2rem; }
.form-card, .stat-card { background: var(--white); padding: 1.5rem; border-radius: var(--radius); box-shadow: var(--shadow); margin-bottom: 1.5rem; }
.data-table { width: 100%; border-collapse: collapse; }
.data-table th { text-align: left; padding: 1rem; background: #f1f5f9; }
.data-table td { padding: 1rem; border-bottom: 1px solid var(--border); }
.btn { padding: 0.6rem 1.2rem; border-radius: var(--radius); cursor: pointer; text-decoration: none; border: none; font-weight: 600; }
.btn-primary { background: var(--primary); color: white; }
.badge { padding: 0.25rem 0.75rem; border-radius: 20px; font-size: 0.75rem; font-weight: 700; }
.badge-paid { background: #dcfce7; color: #166534; }
.badge-overdue { background: #fee2e2; color: #991b1b; }
input, select, textarea { width: 100%; padding: 0.75rem; border: 1px solid var(--border); border-radius: var(--radius); margin-top: 0.5rem; }