A CSS-only version of fancy 2D background gradient
background: linear-gradient( rgba(255,0,255,0.5), rgba(255,255,0,0.5), rgba(0,255,255,0.5), rgba(255,0,255,0.5)), linear-gradient(to right, #f00, #0f0, #00f);
You can see it applied to
<body> element on this very page.
Maybe not as nice, but it definitely works!
Inspired by this (archived) article, but has next-to-nothing in common. (Although it worth reading, too!)