tListener('change', function(event) {
        const file = event.target.files[0];
        if (file) {
            const reader = new FileReader();
            reader.onload = function(e) {
                const preview = document.getElementById('thumbnail-preview');
                preview.innerHTML = `<img src="${e.target.result}" alt="Course Thumbnail" class="w-24 h-24 rounded-lg shadow-md">`;
            };
            reader.readAsDataURL(file);
        }
    });

            document.getElementById('cr