How do I use both a CSS3 gradient and a background image - css

Question

I've seen a million people do it, but I haven't been able to get it to work.
background: -webkit-linear-gradient(left top, black, #333333 85%, gray), url('/img/helix.png');
I've tried with the order reversed and with background-image, still nothing.
I saw one person use:
body:before {
content: " ";
width: 100%;
height: 100%;
position: absolute;
z-index: -1;
top: 0;
left: 0;
background: -webkit-linear-gradient(left top, black, #333333 85%, gray);
}
But there has to be a better way...
Updated code:
In an ID for the image div:
height: 100%;
width: 100%;
background: transparent url('/img/helix-white.png') no-repeat;
In the CSS for the body element:
background: -webkit-linear-gradient(left top, black, #333333 85%, gray);
background: -moz-linear-gradient(left top, black, #333333 85%, gray);
background: -ms-linear-gradient(left top, black, #333333 85%, gray);
background: -o-linear-gradient(left top, black, #333333 85%, gray);
background: linear-gradient(left top, black, #333333 85%, gray);
Update 2:
I used a div with the image in it with CSS for positioning:
<div id="backgroundImage">
<img src="img/helix-white.png" alt=" " />
</div>
#backgroundImage
{
position: fixed;
bottom: 10%;
left: 7%;
opacity:0.4;
filter:alpha(opacity=40);
-webkit-transform: rotateZ(20deg);
-moz-transform: rotateZ(20deg);
-ms-transform: rotateZ(20deg);
-o-transform: rotateZ(20deg);
transform: rotateZ(20deg);
}
And in the body CSS for the gradient:
height: 100%;
background: -webkit-linear-gradient(left top, black, #333333 85%, gray);
background: -moz-linear-gradient(left top, black, #333333 85%, gray);
background: -ms-linear-gradient(left top, black, #333333 85%, gray);
background: -o-linear-gradient(left top, black, #333333 85%, gray);
background: linear-gradient(left top, black, #333333 85%, gray);

Answer 1

Why not have a div with the background gradient then another div inside with a background image. If the background image is a .png with transparency or doesn't fill the div, you'll be able to see the gradient behind it.
e.g.
<div id="gradient">
<div id="image">
Your content here.
</div>
</div>
CSS
#gradient {
background: -webkit-linear-gradient(left top, black, #333333 85%, gray); }
#image {
background: transparent url('your image here') center center no-repeat; }
On another note, you should use a full range of gradient options to support all browsers (not just webkit). I'd recommend using a CSS3 gradient generator for the code:
http://www.colorzilla.com/gradient-editor/

Answer 2

as mentioned, be sure you're checking your stuff in either Safari or an older version of Chrome. They both use(d) webkit as the rendering engine.