How can I tint a background image with CSS?

I have a background image set up through CSS.

html {
background-image: url('../img/cello.jpg');
background-attachment: fixed;
background-size: 100%;
}

I plan on having a different background image for different pages of the website: so it's important that text is legible over it. Right now I've got a translucent black background to my #main content box in the middle like this in order to ensure legibility:

#main {
background: rgba(0, 0, 0, 0.5);
}

What I really want to do, though, is to have that kind of translucent background over the entire background image, because the black box looks a bit clunky. I've tried making a <div id=#tint> which includes the whole HTML document and giving rgba(0, 0, 0, 0.5) to #tint, but that doesn't work at all--I can either get nothing to change or I can get the entire background to become a simple grey with no background image visible at all. Is this simply not possible?

Use background-blend-mode for a simple tint

You can use the background-blend-mode css property:

.background-tint {
  background-color: rgba(200,100,0,.5); /* Tint color */
  background-blend-mode: multiply;
}

Place it on any element with a background image and you're good to go.

The property is well supported in modern browsers NOT including IE 11. For non supporting browsers you can use a polyfill.

Working demo

Other Options

Use filter for a complex tint

You can use the filter css property:

.background-tint {
  filter: sepia(100%) saturate(200%) brightness(70%) hue-rotate(330deg);
}

Place it on any element with a background image and you're good to go. In order to change the color change the hue-rotate value.

The property is well supported in modern browsers NOT including IE 11.

Working demo

Use a flat linear-gradient and a multiple background overlay

.background-tint {
  background-image: 
    linear-gradient( rgba(0,0,0,.5), rgba(0,0,0,.5) ),
    url('http://placehold.it/420')
}

I think this is the most widely used technique but it has the downside of being hardcoded i.e. you can't just take a class, stick it on an element and make a tint.

You could make this into a less or sass mixin, something like:

less

.background-tint(@tint-color, @image-url) {
  background-image: 
    linear-gradient( @tint-color, @tint-color ),
    url( @image-url )
}

sass

@mixin background-tint($tint_color, $image_url) {
  background-image: 
    linear-gradient( $tint_color, $tint_color ),
    url( $image_url )
}

Working demo

Use a transparent background

.background-tint { position: relative; }

.background-tint::after {
  content: "";
  position: absolute;
  top: 0;
  left: 0;
  right: 0;
  bottom: 0;
  width: 100%;
  height: 100%;
  background-color: rgba(0,0,0,.5);
}

This method has the advantage of working on most browsers and is just a nice class you add to any element. The downside is that if you have anything else inside of that element you will have to wrap it in a div with some kind of positioning position: relative would work best.

Example:

<div class="background-tint">
  <div class="u-relative">Some text here</div>
</div>

.u-relative { position: relative; }

Working Demo

I think you need to create an overlay element (potentially div) which has the sought translucent background. Something like:

.overlay {
    z-index: 1;
    height: 100%;
    width: 100%;
    position: fixed;
    overflow: auto;
    top: 0px;
    left: 0px;
    background: rgba(0, 0, 0, 0.7); /*can be anything, of course*/
}

And of course, a little demo: little link.