Dragon Interactive Labs have excellent demos on how javascript can be stretched to create some awesome effects. This post details how the dragon fish demo login screen is done using pure javascript. The colors around the login box and the glow are done using background images and changing its position. The first layer is this image that is set as a background image changing its left all the while.
On top of this div are the masks for the four corners and the four sides. These have images with semitransparent pngs that are respinsible for the glow effect. There is also a mask in the middle that masks the majority of the background.
It is above this layer that regular fieldset containing the username and password fields. You can see this effect if you move the third element with "map" classname with to an absolute position and 200 px left. The javascript constantly move the huge image to left, creating the effect.
