Inténtalo tú mismo - CSS Reference gradient-linear

<!DOCTYPE html>
<html>
<head>
<style>
#grad1 {
    height: 100px;
    background: -webkit-linear-gradient(0deg, red, blue); /* For Safari 5.1 to 6.0 */
    background: -o-linear-gradient(0deg, red, blue); /* For Opera 11.1 to 12.0 */
    background: -moz-linear-gradient(0deg, red, blue); /* For Firefox 3.6 to 15 */
    background: linear-gradient(0deg, red, blue); /* Standard syntax (must be last) */
}

#grad2 {
    height: 100px;
    background: -webkit-linear-gradient(90deg, red, blue); /* For Safari 5.1 to 6.0 */
    background: -o-linear-gradient(90deg, red, blue); /* For Opera 11.1 to 12.0 */
    background: -moz-linear-gradient(90deg, red, blue); /* For Firefox 3.6 to 15 */
    background: linear-gradient(90deg, red, blue); /* Standard syntax (must be last) */
}

#grad3 {
    height: 100px;
    background: -webkit-linear-gradient(180deg, red, blue); /* For Safari 5.1 to 6.0 */
    background: -o-linear-gradient(180deg, red, blue); /* For Opera 11.1 to 12.0 */
    background: -moz-linear-gradient(180deg, red, blue); /* For Firefox 3.6 to 15 */
    background: linear-gradient(180deg, red, blue); /* Standard syntax (must be last) */
}

#grad4 {
    height: 100px;
    background: -webkit-linear-gradient(-90deg, red, blue); /* For Safari 5.1 to 6.0 */
    background: -o-linear-gradient(-90deg, red, blue); /* For Opera 11.1 to 12.0 */
    background: -moz-linear-gradient(-90deg, red, blue); /* For Firefox 3.6 to 15 */
    background: linear-gradient(-90deg, red, blue); /* Standard syntax (must be last) */
}
</style>
</head>
<body>

<h3>Linear Gradients - Using Different Angles</h3>
<div id="grad1" style="color:white;text-align:center;">0deg</div><br>
<div id="grad2" style="color:white;text-align:center;">90deg</div><br>
<div id="grad3" style="color:white;text-align:center;">180deg</div><br>
<div id="grad4" style="color:white;text-align:center;">-90deg</div>

<p><strong>Note:</strong> Internet Explorer 9 and earlier versions do not support gradients.</p>

</body>
</html>