Resizing video in mobile view.

Hey! Hello from Barcelona, Spain. This is my first time here, so thanks in advance for any help.

I built my site with a wordpress template and did the design by myself.
The problem started to adapt the site to mobile.

I hired a designer to make it as good as possible, but now I would like to make some modifications
in order to add some media, and I need some CSS help with it.

Please, I would like to know how to resize a video with additional CSS.
The video works as a background. It´s a link from Vimeo instead of a colour.

I have several videos in my site, and on my mobile they are all different sizes.

This is the page. There are two videos.
http://revitalrecords.es/artists-production/

Both videos are very big on mobile. I would like to fix that.
How can I do it?

Thanks very much!!