:root {
            --primary-color: #3498db;
            --secondary-color: #2980b9;
            --accent-color: #e67e22;
            --bg-color: #f4f7f6;
            --text-dark: #2c3e50;
            --white: #ffffff;
            --vowel-bg: #e1f5fe;
        }

        body {
            font-family: 'Pyidaungsu', sans-serif;
            margin: 0;
            background-color: var(--bg-color);
            color: var(--text-dark);
            line-height: 1.6;
        }

        /* --- Navbar --- */
        .navbar {
            background: var(--primary-color);
            color: white;
            padding: 15px 20px;
            display: flex;
            justify-content: space-between;
            align-items: center;
            position: sticky;
            top: 0;
            z-index: 1000;
        }

        .menu-btn {
            background: rgba(255,255,255,0.2);
            border: none;
            color: white;
            padding: 8px 15px;
            border-radius: 5px;
            cursor: pointer;
        }

        /* --- Sidebar --- */
        .sidebar {
            height: 100%;
            width: 0;
            position: fixed;
            z-index: 2000;
            top: 0;
            left: 0;
            background-color: #34495e;
            overflow-x: hidden;
            transition: 0.4s;
            padding-top: 60px;
        }

        .sidebar a {
            padding: 12px 25px;
            text-decoration: none;
            font-size: 1.1rem;
            color: #bdc3c7;
            display: block;
        }

        .sidebar a:hover { background: var(--secondary-color); color: white; }

        .close-btn { position: absolute; top: 10px; right: 25px; font-size: 30px; color: white; cursor: pointer; }

        /* --- Main Content --- */
        .container {
            max-width: 800px;
            margin: 20px auto;
            padding: 15px;
        }

        .lesson-header {
            background: var(--primary-color);
            color: white;
            text-align: center;
            padding: 15px;
            border-radius: 15px;
            margin-bottom: 25px;
        }

        /* --- Lesson Box --- */
        .lesson-box {
            background: var(--white);
            border-radius: 15px;
            padding: 20px;
            box-shadow: 0 4px 15px rgba(0,0,0,0.05);
            margin-bottom: 20px;
        }

        .word-group {
            display: grid;
            grid-template-columns: repeat(3, 1fr);
            gap: 12px;
            text-align: center;
            font-size: 1.4rem;
            font-weight: bold;
        }

        .word-item {
            padding: 10px;
            background: var(--vowel-bg);
            border-radius: 10px;
            border: 1px solid #b3e5fc;
        }

        .special-chars {
            margin: 20px 0;
            padding: 15px;
            background: #fff3e0;
            border: 2px solid #ffcc80;
            border-radius: 10px;
            text-align: center;
            font-size: 1.5rem;
            word-spacing: 20px;
            color: #e65100;
        }

        /* --- Exercise Section --- */
        .reading-title {
            color: var(--secondary-color);
            font-weight: bold;
            margin-bottom: 10px;
            display: block;
            border-bottom: 2px solid #eee;
            padding-bottom: 5px;
        }

        .reading-text {
            font-size: 1.2rem;
            line-height: 2.2;
            white-space: pre-wrap;
        }

        .highlight-box {
            background: #fdfdfd;
            border: 1px solid #eee;
            padding: 15px;
            border-radius: 10px;
            margin-top: 10px;
            display: flex;
            flex-wrap: wrap;
            gap: 15px;
            justify-content: center;
        }

        /* --- Footer --- */
        footer { background: #2d3436; color: white; text-align: center; padding: 20px; margin-top: 40px; }

        @media (max-width: 480px) {
            .word-grid { grid-template-columns: repeat(2, 1fr); font-size: 1.1rem; }
            .reading-text { font-size: 1.1rem; }
        }