[css] How to add a color overlay to a background image?

I have seen this question a lot both on SO and the Web. But none of them has been what I am looking for.

How do I add a color-overlay to a background image using CSS only?

Example HTML:

<div class="testclass">
</div>

Example CSS:

.testclass {
    background-image: url("../img/img.jpg");
}

Please note:

• I want to solve this by only using CSS. i.e I do NOT want to add a child div within the div "testclass" for the color overlay.

• This should not be a "hover effect" I want to simply just add a color-overay to the background image.

• I want to be able to use opacity i.e. I am looking for a solution that allows RGBA color.

• I am looking for just one color, lets say black. Not a gradient.

Is this possible? (I would be surprised if not, but I have not been able to find anything about this), and if so what the best way to accomplish this?

All suggestions and advice are appreciated!

You can use a pseudo element to create the overlay.

.testclass {
  background-image: url("../img/img.jpg");
  position: relative;
}
.testclass:before {
  content: "";
  position: absolute;
  left: 0; right: 0;
  top: 0; bottom: 0;
  background: rgba(0,0,0,.5);
}

background-image takes multiple values.

so a combination of just 1 color linear-gradient and css blend modes will do the trick.

.testclass {
    background-image: url("../images/image.jpg"), linear-gradient(rgba(0,0,0,0.5),rgba(0,0,0,0.5));
    background-blend-mode: overlay;
}

note that there is no support on IE/Edge for CSS blend-modes at all.

Try this, it's simple and clear. I have found it from here : https://css-tricks.com/tinted-images-multiple-backgrounds/

.tinted-image {

  width: 300px;
  height: 200px;

  background: 
    /* top, transparent red */ 
    linear-gradient(
      rgba(255, 0, 0, 0.45), 
      rgba(255, 0, 0, 0.45)
    ),
    /* bottom, image */
    url(https://s3-us-west-2.amazonaws.com/s.cdpn.io/3/owl1.jpg);
}