:root {
            --primary-color: #0d47a1;
            --secondary-color: #1565c0;
            --topbar-bg: #1a237e;
            --accent-color: #d32f2f;
            --bg-color: #f4f6f9;
            --text-color: #333333;
            --light-bg: #ffffff;
        }

        body {
            font-family: 'Segoe UI', Tahoma, Geneva, Verdana, sans-serif;
            line-height: 1.6;
            color: var(--text-color);
            background-color: var(--bg-color);
            margin: 0;
            padding: 0;
        }

        .container {
            width: 85%;
            max-width: 1200px;
            margin: auto;
        }

        /* Main Content Layout */
        .main-layout {
            display: grid;
            grid-template-columns: 3fr 1fr;
            gap: 20px;
            margin: 25px auto;
        }

        .content-area, .sidebar {
            background: var(--light-bg);
            padding: 25px;
            border-radius: 4px;
            box-shadow: 0 1px 3px rgba(0,0,0,0.1);
        }

        h2, h3 {
            color: var(--primary-color);
            border-bottom: 2px solid #e0e0e0;
            padding-bottom: 8px;
            margin-top: 0;
        }

        /* Sub-menu Indentation */
        .side-menu .sub-menu {
            padding-left: 15px;
        }

        .side-menu {
            list-style: none;
            padding: 0;
            margin: 0 0 18px 0;
        }

        .side-menu li {
            border-bottom: 1px solid #eee;
        }

        .side-menu a {
            color: var(--text-color);
            text-decoration: none;
            display: block;
            padding: 7px 0;
            transition: color 0.2s;
        }

        .side-menu a:hover {
            color: var(--secondary-color);
            font-weight: bold;
        }

        /* Sidebar Elements */
        .btn-submit {
            display: block;
            background-color: var(--accent-color);
            color: #ffffff;
            text-align: center;
            padding: 12px;
            text-decoration: none;
            font-weight: bold;
            border-radius: 4px;
            margin-bottom: 20px;
            transition: background 0.3s;
        }

        .btn-submit:hover {
            background-color: #b71c1c;
        }

        @media (max-width: 768px) {
            .main-layout {
                grid-template-columns: 1fr;
            }
        }