Gradiente Radial CSS3

[mdk]

Aquí tienes un ejemplo que se te adapta a la ventana.

Código:

body {
background: #000000; /* fallback for non-supporting browsers */  
    background-image: -webkit-gradient(radial, center center, 0, center center, 141, from(black), to(white), color-stop(25%, blue), color-stop(40%, green), color-stop(60%, red), color-stop(80%, purple)); /* old WebKit Syntax */  
    background-image: -webkit-radial-gradient(center center, circle contain, black 0%, blue 25%, green 40%, red 60%, purple 80%, white 100%); /* New WebKit syntax */  
    background-image: -moz-radial-gradient(center center, circle contain, black 0%, blue 25%, green 40%, red 60%, purple 80%, white 100%);  
    background-image: -ms-radial-gradient(center center, circle contain, black 0%, blue 25%, green 40%, red 60%, purple 80%, white 100%); /* IE10+ */  
    background-image: -o-radial-gradient(center center, circle contain, black 0%, blue 25%, green 40%, red 60%, purple 80%, white 100%); /* Opera (13?) */  
}