WordPress video widget not working

Hi, I'n not shure if this is an issue of my theme. When I try to use the video widget, which comes with wordpress, then the following happens: - I add the widget to my sidebar - I add an title to the widget - I add a mp4 video to the widget - I can see and play the video in the widget - Back on the Website, there is only an empty white box with the title, but no video. Could you please check if this is an issue of the theme "Catch Flames Free? Thank you for your effort Bernhard