[Plugin: Artiss YouTube Embed] Videos not re-scaling ("responsive")

I’m trying to make my site as “responsive” as possible by having my embedded YouTube videos scale down to the users’ screen. Your description of the plugin says it does that and that’s why I went with it. Is there something I’m supposed to check off or do extra to make this feature happen?

An example is at:

http://alegremedia.com/commercials/

The video is staying the same size, both when I adjust the browser size settings and when I view it on my Android phone. Any assistance is most appreciated, thanks.

http://wordpress.org/extend/plugins/youtube-embed/