Embed a Youtube video on the home page

This video is to be accessed via the footer link "Demo" and lies over the login card. Make sure that the embedding is responsive for each screen size.

Be inspired by Bootstrap's embed.scss:

Doc: https://getbootstrap.com/docs/3.3/components/#responsive-embed

Code: https://github.com/twbs/bootstrap/blob/master/scss/helpers/_embed.scss

Or this one: https://martinahonecker.com/youtube-videos-responsive-einbinden/

I will create a screencast that shows how to create a session and how to write a comment, filter comments, sort them and mark them as "Right", "Favorite" and "Seen".