background: -webkit-linear-gradient(red, green, blue);
background: -o-linear-gradient(red, green, blue);
background: -moz-linear-gradient(red, green, blue);
background: linear-gradient(red, green, blue);
background: -webkit-linear-gradient(red, orange, yellow, green, blue, indigo, violet);
background: -o-linear-gradient(red, orange, yellow, green, blue, indigo, violet);
background: -moz-linear-gradient(red, orange, yellow, green, blue, indigo, violet);
background: linear-gradient(red, orange, yellow, green, blue, indigo, violet);