Help Fixing Youtube iFrame Responsive Display

I have a responsive theme with a youtube iFrame inside a simple Text widget:

<iframe src=”//www.youtube.com/embed/rIc5CRWJVCs?vq=hd720;rel=0;showinfo=0;color=white;controls=2;modestbranding=1;autoplay=1; frameborder=0; fs=1;” height=”506″ width=”900″></iframe>

http://bit.ly/1nTclSo

The iFrame is not scaling nicely on mobile devices…. could you help me fix it?

Thanks.