Diagonal starts at top left and right button. You can try to run the following code to implement diagonal gradients in CSS3 −
<html>
<head>
<style>
#grad1 {
height: 100px;
background: -webkit-linear-gradient(left top, red , blue);
background: -o-linear-gradient(bottom right, red, blue);
background: -moz-linear-gradient(bottom right, red, blue);
background: linear-gradient(to bottom right, red , blue);
}
</style>
</head>
<body>
<div id = "grad1"></div>
</body>
</html>