I'm looking for a good fallback for both HTML5 and CSS3 so I could use it and it would still look ok in other browsers.
When talking about HTML5 or CSS3, you should head over to:
As can be seen, we are still far far away from using that.
Also, since old versions of the browsers won't support HTML5 or CSS3, however, you can do what is known as:
Progressive Enhancement and Graceful Degradation
Here are some resources also: