There’s a fabulous new design in the CSS Zen Garden, created by Menz Meyer. Boot up a browser that isn’t IE/Win and check out the transition effect as you scroll the page horizontally. (For those of you who don’t know, the CSS Zen Garden demonstrates to the world just how powerful and creative style sheets can be. All the beautiful designs linked to have the same underlying HTML, just a different style sheet.)
Well, the afore-mentioned transition is achieved by applying a PNG image with varying alpha transparency. Alpha transparency is supported natively by all modern browsers except one. For some cross-browser transparent PNG techniques see A List Apart.