@import url('https://fonts.googleapis.com/css2?family=Orbitron:wght@600&family=Quicksand:wght@500&display=swap');
                @import url('https://fonts.googleapis.com/css2?family=Orbitron:wght@600&family=Quicksand:wght@500&display=swap');
        
        * {
            margin: 0;
            padding: 0;
            box-sizing: border-box;
        }
        
        body {
            font-family: 'Arial', sans-serif;
            background: #f4f4f4;
            color: #333;
        }
        
        .lingua-header {
            background: linear-gradient(to right, #497979, #3e6666);
            color: white;
            box-shadow: 0 4px 12px rgba(0,0,0,0.2);
            text-align: center;
            padding-top: 1rem;
            padding-bottom: 1rem;
            position: relative;
        }
        
        .lingua-header .btn {
            border-color: #ffffff;
            color: #ffffff;
        }
        
        .lingua-header .btn:hover {
            background-color: rgba(255, 255, 255, 0.2);
            border-color: #ffffff;
            color: #ffffff;
        }
        
        .lingua-header .btn span.bi {
            font-size: 1.5rem;
        }
        
        .lingua-title {
            font-family: 'Orbitron', sans-serif;
            font-size: 48px;
            letter-spacing: 2px;
            margin: 0;
            text-shadow: 2px 2px 6px rgba(0,0,0,0.4);
            color: #ffffff;
        }
        
        .lingua-title span {
            color: #d4ffeb;
            font-family: 'Quicksand', sans-serif;
            font-weight: bold;
        }
        
        .main-container {
            display: flex;
            max-width: 1400px;
            margin: 30px auto;
            gap: 25px;
            padding: 0 20px;
        }
        
        .sidebar {
            width: 280px;
            background: white;
            border: 1px solid #ddd;
            height: fit-content;
        }
        
        .category {
            border-bottom: 1px solid #e0e0e0;
        }
        
        .category-header {
            padding: 14px 20px;
            background: #fafafa;
            cursor: pointer;
            font-weight: 500;
            color: #3F6969;
            border-left: 3px solid transparent;
            transition: all 0.2s;
            position: relative;
        }
        
        .category-header:after {
            content: '▼';
            position: absolute;
            right: 20px;
            font-size: 10px;
            transition: transform 0.2s;
        }
        
        .category-header.active:after {
            transform: rotate(180deg);
        }
        
        .category-header:hover {
            background: #f0f0f0;
            border-left-color: #3F6969;
        }
        
        .category-items {
            display: none;
            background: white;
        }
        
        .category-items.active {
            display: block;
        }
        
        .pub-item {
            padding: 12px 20px 12px 35px;
            cursor: pointer;
            font-size: 14px;
            color: #555;
            border-left: 3px solid transparent;
            transition: all 0.2s;
        }
        
        .pub-item:hover {
            background: #f8f8f8;
            color: #3F6969;
            border-left-color: #3F6969;
        }
        
        .pub-item.selected {
            background: #e8f4f4;
            color: #3F6969;
            border-left-color: #3F6969;
            font-weight: 500;
        }
        
        .content {
            flex: 1;
            background: white;
            border: 1px solid #ddd;
            min-height: 700px;
        }
        
        .content-header {
            padding: 20px 30px;
            border-bottom: 2px solid #3F6969;
            background: #fafafa;
        }
        
        .content-header h2 {
            font-size: 20px;
            color: #3F6969;
            margin-bottom: 10px;
            word-wrap: break-word;
        }
        
        .content-meta {
            font-size: 14px;
            color: #666;
            line-height: 1.6;
        }
        
        .content-meta p {
            margin: 5px 0;
            word-wrap: break-word;
        }
        
        .download-section {
            padding: 20px 30px;
            background: #f9f9f9;
            border-bottom: 1px solid #e0e0e0;
        }
        
        .btn-download {
            display: inline-block;
            padding: 10px 25px;
            background: #3F6969;
            color: white;
            text-decoration: none;
            font-size: 14px;
            font-weight: 500;
            border-radius: 3px;
            transition: background 0.2s;
        }
        
        .btn-download:hover {
            background: #2d4d4d;
            color: white;
        }
        
        .pdf-container {
            padding: 20px 30px;
        }
        
        .pdf-frame {
            width: 100%;
            height: 70vh;
            border: 1px solid #ddd;
            border-radius: 4px;
        }
        
        .welcome {
            padding: 100px 30px;
            text-align: center;
            color: #888;
        }
        
        .welcome h2 {
            color: #3F6969;
            font-size: 22px;
            margin-bottom: 15px;
        }
        
        .welcome p {
            font-size: 15px;
            line-height: 1.8;
        }

        /* Responsive Design */
        @media (max-width: 992px) {
            .main-container {
                flex-direction: column;
            }
            .sidebar {
                width: 100%;
            }
            .pdf-frame {
                height: 500px;
            }
        }

        @media (max-width: 768px) {
            .lingua-title {
                font-size: 2rem;
            }
            .content-header {
                padding: 15px 20px;
            }
            .content-header h2 {
                font-size: 18px;
            }
            .download-section {
                padding: 15px 20px;
            }
            .pdf-container {
                padding: 15px 20px;
            }
            .pdf-frame {
                height: 400px;
            }
            .welcome {
                padding: 50px 20px;
            }
        }

        @media (max-width: 576px) {
            .main-container {
                margin: 15px auto;
                padding: 0 10px;
                gap: 15px;
            }
            .lingua-header {
                padding: 1rem 0;
            }
            .lingua-title {
                font-size: 1.5rem;
            }
            .category-header {
                padding: 12px 15px;
                font-size: 14px;
            }
            .pub-item {
                padding: 10px 15px 10px 25px;
                font-size: 13px;
            }
            .content-header h2 {
                font-size: 16px;
            }
            .content-meta {
                font-size: 13px;
            }
            .pdf-frame {
                height: 300px;
            }
        }