Up to Contao 4.13: select the content element template ce_download_zeroone or ce_downloads_zeroone (template settings)
Contao 5.0 and later: select the content element template content_element/download/download_zeroone or content_element/downloads/downloads_zeroone (template settings)
Gallery
Select the element type Gallery
Make your settings
Up to Contao 4.13: select the content element template ce_gallery_zeroone (template settings)
Contao 5.0 and later: select the content element template content_element/gallery/gallery_zeroone (template settings)
YouTube video
Select the element type YouTube
Make your settings
Up to Contao 4.13: select the content element template ce_youtube_zeroone (template settings)
Contao 5.0 and later: select the content element template content_element/youtube/youtube_zeroone (template settings)