ColorHexa is a color encyclopedia, with CSS gradients, blends, schemes and more February 3, 2012 - 11:06 pm Color, one of the seven elements of art, is one of the most important aspects of any design.

Well, it's not the best solution, and it's not strictly using CSS, but you could make a small image that contains the transition from 1 color to another, and then stretch it to the desired size ...

Major browsers support CSS3 gradients (including Internet Explorer 10), but with different rendering engines, it's still good to have fallbacks.