How do I combine a background-image and CSS3 gradient on the same element?

One thing to realize is that the first defined background image is topmost in the stack. The last defined image will be bottommost. That means, to have a background gradient behind an image, you would need:

  body {
    background-image: url("http://www.skrenta.com/images/stackoverflow.jpg"), linear-gradient(red, yellow);
    background-image: url("http://www.skrenta.com/images/stackoverflow.jpg"), -webkit-gradient(linear, left top, left bottom, from(red), to(yellow));
    background-image: url("http://www.skrenta.com/images/stackoverflow.jpg"), -moz-linear-gradient(top, red, yellow);
  }

You could also define background positions and background size for the images. I put together a blog post about some interesting things you can do with CSS3 gradients

Multiple backgrounds!

body {
  background: #eb01a5;
  background-image: url("IMAGE_URL"); /* fallback */
  background-image: url("IMAGE_URL"), linear-gradient(#eb01a5, #d13531); /* W3C */
}

These 2 lines are the fallback for any browser that doesn't do gradients. See notes for stacking images only IE < 9 below.

• Line 1 sets a flat background color.
• Line 2 sets the background image fallback.

The final line sets a background image and gradient for browsers that can handle them.

• Line 3 is for all relatively modern browsers.

Nearly all current browsers have support for multiple background images and css backgrounds. See http://caniuse.com/#feat=css-gradients for browser support. For a good post on why you don't need multiple browser prefixes, see http://codepen.io/thebabydino/full/pjxVWp/

Layer Stack

It should be noted that the first defined image will be topmost in the stack. In this case, the image is on TOP of the gradient.

For more information about background layering see http://www.w3.org/TR/css3-background/#layering.

Stacking images ONLY (no gradients in the declaration) For IE < 9

IE9 and up can stack images this same way. You could use this to create a gradient image for ie9, though personally, I wouldn't. However to be noted when using only images, ie < 9 will ignore the fallback statement and not show any image. This does not happen when a gradient is included. To use a single fallback image in this case I suggest using Paul Irish's wonderful Conditional HTML element along with your fallback code:

.lte9 #target{ background-image: url("IMAGE_URL"); }

Background position, sizing etc.

Other properties that would apply to a single image may also be comma separated. If only 1 value is supplied, that will be applied to all stacked images including the gradient. background-size: 40px; will constrain both the image and the gradient to 40px height and width. However using background-size: 40px, cover; will make the image 40px and the gradient will cover the element. To only apply a setting to one image, set the default for the other: background-position: 50%, 0 0; or for browsers that support it use initial: background-position: 50%, initial;

You may also use the background shorthand, however this removes the fallback color and image.

body{
    background: url("IMAGE_URL") no-repeat left top, linear-gradient(#eb01a5, #d13531);
}

The same applies to background-position, background-repeat, etc.

If you also want to set background position for your image, than you can use this:

background-color: #444; // fallback
background: url('PATH-TO-IMG') center center no-repeat; // fallback

background: url('PATH-TO-IMG') center center no-repeat, -moz-linear-gradient(top, @startColor, @endColor); // FF 3.6+
background: url('PATH-TO-IMG') center center no-repeat, -webkit-gradient(linear, 0 0, 0 100%, from(@startColor), to(@endColor)); // Safari 4+, Chrome 2+
background: url('PATH-TO-IMG') center center no-repeat, -webkit-linear-gradient(top, @startColor, @endColor); // Safari 5.1+, Chrome 10+
background: url('PATH-TO-IMG') center center no-repeat, -o-linear-gradient(top, @startColor, @endColor); // Opera 11.10
background: url('PATH-TO-IMG') center center no-repeat, linear-gradient(to bottom, @startColor, @endColor); // Standard, IE10

or you can also create a LESS mixin (bootstrap style):

#gradient {
    .vertical-with-image(@startColor: #555, @endColor: #333, @image) {
        background-color: mix(@startColor, @endColor, 60%); // fallback
        background-image: @image; // fallback

        background: @image, -moz-linear-gradient(top, @startColor, @endColor); // FF 3.6+
        background: @image, -webkit-gradient(linear, 0 0, 0 100%, from(@startColor), to(@endColor)); // Safari 4+, Chrome 2+
        background: @image, -webkit-linear-gradient(top, @startColor, @endColor); // Safari 5.1+, Chrome 10+
        background: @image, -o-linear-gradient(top, @startColor, @endColor); // Opera 11.10
        background: @image, linear-gradient(to bottom, @startColor, @endColor); // Standard, IE10
    }
}