* {
            margin: 0;
            padding: 0;
            box-sizing: border-box;
            font-family: 'Segoe UI', Tahoma, Geneva, Verdana, sans-serif;
        }
        
        /* HEADER STYLES */
        .header {
            background-color: #2c3e50;
            color: white;
            padding: 15px 0;
            box-shadow: 0 2px 5px rgba(0,0,0,0.1);
        }
        
        .header-content {
            max-width: 1200px;
            margin: 0 auto;
            display: flex;
            justify-content: space-between;
            align-items: center;
            padding: 0 20px;
        }
        
        .header-content a {
            display: flex;
            align-items: center;
            text-decoration: none;
            color: white;
        }
        
        .header-content img {
            height: 50px;
            margin-right: 15px;
        }
        
        .header-title {
            font-size: 1.5rem;
            font-weight: bold;
        }
        
        .download-button {
            background-color: #e74c3c;
            color: white;
            border: none;
            padding: 10px 20px;
            border-radius: 4px;
            cursor: pointer;
            font-weight: bold;
            transition: background 0.3s;
        }
        
        .download-button:hover {
            background-color: #c0392b;
        }
        .teacher-badge {
            background-color: #3498db;
            color: white;
            padding: 3px 8px;
            border-radius: 4px;
            font-size: 0.8rem;
            display: inline-block;
            margin-left: 10px;
        }
        
        /* MAIN CONTENT STYLES */
        .container {
            max-width: 1200px;
            margin: 30px auto;
            padding: 0 20px;
        }
        
        .book-header {
            display: flex;
            gap: 30px;
            margin-bottom: 30px;
            flex-wrap: wrap;
        }
        
        .book-cover {
            width: 250px;
            height: auto;
            max-height: 350px;
            object-fit: contain;
            border-radius: 8px;
            
        }
        
        .book-header h1 {
            font-size: 2rem;
            color: #2c3e50;
            margin-bottom: 10px;
        }
        
        .book-header p {
            margin-bottom: 8px;
            color: #555;
        }
        
        .book-header strong {
            color: #2c3e50;
        }
        
        .download-btn {
            display: inline-block;
            padding: 10px 20px;
            background: #3498db;
            color: white;
            text-decoration: none;
            border-radius: 4px;
            margin-top: 15px;
            transition: background 0.3s;
        }
        
        .download-btn:hover {
            background: #2980b9;
        }
        
        .pdf-viewer-container {
            width: 100%;
            height: 80vh;
            margin: 40px 0;
            border: 1px solid #ddd;
            border-radius: 8px;
            overflow: hidden;
            position: relative;
        }
        
        .pdf-viewer {
            width: 100%;
            height: 100%;
            border: none;
            position: absolute;
            top: 0;
            left: 0;
            right: 0;
            bottom: 0;
        }
        
        .alert {
            padding: 15px;
            background: #f8d7da;
            color: #721c24;
            border-radius: 4px;
            margin: 20px 0;
            display: flex;
            align-items: center;
            gap: 10px;
        }
        
        .back-btn {
            display: inline-flex;
            align-items: center;
            gap: 5px;
            padding: 10px 20px;
            background: #f8f9fa;
            color: #2c3e50;
            text-decoration: none;
            border-radius: 4px;
            margin-top: 20px;
            border: 1px solid #ddd;
            transition: all 0.3s;
        }
        
        .back-btn:hover {
            background: #e9ecef;
        }
        
        /* FOOTER STYLES */
        .site-footer {
            background-color: #2c3e50;
            color: white;
            padding: 40px 0 20px;
            margin-top: 50px;
        }
        
        .footer-content {
            max-width: 1200px;
            margin: 0 auto;
            padding: 0 20px;
        }
        
        .footer-brand {
            margin-bottom: 30px;
        }
        
        .footer-title {
            font-size: 1.5rem;
            margin-bottom: 15px;
        }
        
        .footer-social {
            display: flex;
            gap: 15px;
        }
        
        .footer-social a {
            color: white;
            font-size: 1.5rem;
            transition: color 0.3s;
        }
        
        .footer-social a:hover {
            color: #3498db;
        }
        
        .footer-info {
            border-top: 1px solid rgba(255,255,255,0.1);
            padding-top: 20px;
            text-align: center;
        }
        
        .copyright, .credits {
            font-size: 0.9rem;
            color: rgba(255,255,255,0.7);
            margin-bottom: 5px;
        }

        /* RESPONSIVE STYLES */
        @media screen and (max-width: 768px) {
            .header-content {
                flex-direction: column;
                text-align: center;
                gap: 15px;
            }

            .header-content img {
                margin-right: 0;
                margin-bottom: 10px;
            }

            .book-header {
                flex-direction: column;
                align-items: center;
                text-align: center;
            }

            .book-cover {
                width: 200px;
            }

            .book-header h1 {
                font-size: 1.5rem;
            }

            .pdf-viewer-container {
                height: 60vh;
                max-width: 100%;
                overflow-x: auto;
            }

            .pdf-viewer {
                max-width: 100%;
                height: 100%;
            }

            .footer-content {
                text-align: center;
            }

            .footer-social {
                justify-content: center;
            }
        }

        @media screen and (max-width: 480px) {
            .header-title {
                font-size: 1.2rem;
            }

            .download-button,
            .download-btn {
                width: 100%;
                text-align: center;
            }

            .book-cover {
                width: 150px;
            }

            .book-header h1 {
                font-size: 1.2rem;
            }

            .pdf-viewer-container {
                height: 50vh;
                max-width: 100%;
                overflow-x: auto;
            }

            .pdf-viewer {
                max-width: 100%;
                height: 100%;
            }

            .alert {
                flex-direction: column;
                text-align: center;
            }

            .back-btn {
                width: 100%;
                justify-content: center;
            }
        }