> {
                const thumbnailDiv = document.createElement('div');
                thumbnailDiv.className = `thumbnail ${index === currentSlideIndex ? 'active' : ''}`;
                thumbnailDiv.onclick = () => goToSlide(index);
                thumbnailDiv.setAttribute('data-slide-index', index);

                thumbnailDiv.innerHTML = `
                    <iframe srcdoc="${slide.html_content.replace(/"/g, '&quot;')}" title="Slide ${index + 1}"></iframe>
                    <div class="thumbnail-