How to place an HTML5 animation in a widget?

How do I go about adding an HTML5 animation to a widget area. I have the HTML which I have added to a text box in the widget area. This displays the animation but then the rest of the page stops working. Why might this be? I'm replacing a flash animation which was easy to get to work, but I am finding the advice on HTML5 animations to be confusing.

See original post by Fox Robinson