CSS: background color with opacity on background image

Question

I am trying to assign a background-image and a background-color to a div. There are many SO answers (like this) with the solution to either combine them in background:

background: rgba(255,0,0,0.5) url('http://placehold.it/100x100');

Or use separate properties:

background-color: rgba(255,0,0,0.5);
background-image: url('http://placehold.it/100x100');

Neither of the above are working for me (tested in Firefox and Chrome) - I breifly see the correct background color and then it disappears and all that is left is the image. What does work for some reason is:

 background: linear-gradient(to bottom, rgba(255,0,0,0.5) 0%, rgba(255,0,0,0.5) 100%), url('http://placehold.it/100x100');

Any idea why these solutions are not working?

UPDATE To better clarify what I am looking for: The color of the div is constantly changing, so I need to be able to dynamically and easily update an inline style with javascript. I was hoping there was a simple solution (as there was in 2011) using the standard background properties. If not, I'll set a linear gradient. It is a bit clunky, but it seems to work fine.

UPDATE2 In the end, I discovered that setting a gradient to the background-image was 3 times slower than setting a background-color property. Because this was part of a color picker, it created an unacceptable lag with mouse movement. I ended up using nested divs and keeping the image constant in the outer div and changing the color in the inner div.

Here is a demo:

#div1 {
  height: 100px;
  width: 100px;
  background-color: rgba(255,0,0,0.5);
  background-image: url('http://placehold.it/100x100');
}

#div2 {
  height: 100px;
  width: 100px;
  background: linear-gradient(to bottom, rgba(255,0,0,0.5) 0%, rgba(255,0,0,0.5) 100%), url('http://placehold.it/100x100');
}

<div id="div1">
</div>

<div id="div2">
</div>

Answer 1

try this code

.background {
    background:url('http://placehold.it/100x100');
    position: relative;
    height: 100px;
  width: 100px;
}

.layer {
    background-color: rgba(75, 86, 160, 0.7);
    position: absolute;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
}

<div class="background">
    <div class="layer">
    </div>
</div>