I've tried multiple times to apply the following piece of code in a CSS document:

display: block;
width: 500px;
margin: 500px auto;
padding: 15px;
text-align: center;
border: 4px solid blue;
background: -webkit-linear-gradient(top,black,white);
outline: 7px solid red;

Everything appears correctly, except the gradient. I have CS6 Live View turned on, and it still refuses to appear. All I get in my box is a white background, as opposed to the black to white gradient. However, when I type the same line of code into the trial of Coda 2 I downloaded, it works perfectly. Is there anything I can do to resolve the issue?