Edit in JSFiddle

#grad {
  width: 300px;
  height: 100px;
  border: 2px solid;
  background: -moz-linear-gradient( left, red 25%, blue 75% );
  background: -webkit-gradient( linear, left center, right center, color-stop( 25%, red ), color-stop( 75%, blue ) );
}

<div id="grad"></div>