ANSWER:

You could try the following syntax instead:

-o-transition-property: background-color;
-o-transition-duration: 4s;

I just modified the fiddle and this indeed works in Opera 11.62. In fact, it appears you could just use the shorthand form, but include -color to make it work with Opera:

-o-transition: background-color 5s;

Source: http://dev.opera.com/articles/view/css3-transitions-and-2d-transforms/

by Jonathan Sampson from http://stackoverflow.com/questions/10354171