How to overlay image with color in CSS?

Objective

I want a color overlay on this header element. How can I do this with CSS?

Code

#header {
  /* Original url */
  /*background: url(../img/bg.jpg) 0 0 no-repeat fixed;*/
  background: url(https://fakeimg.pl/250x100/) 0 0 no-repeat fixed;
  height: 100%;
  overflow: hidden;
  color: #FFFFFF
}

<header id="header">
  <div class="row">
    <div class="col-xs-12">
      ...
    </div>
  </div>
</header>

You should use rgba for overlaying your element with photos.rgba is a way to declare a color in CSS that includes alpha transparency support. you can use .row as an overlayer like this:

#header {
    background: url(../img/bg.jpg) 0 0 no-repeat fixed;
    height: 100%;
    overflow: hidden;
    color: #FFFFFF
 }

.row{
    background: rgba(39,62,84,0.82);
    overflow: hidden;
    height: 100%;
    z-index: 2;
}

You can do that in one line of CSS.

background: linear-gradient(to top, #3204fdba, #9907facc), url(https://picsum.photos/1280/853/?random=1) no-repeat top center;

Also hover on the color in VS Code, and click on the color to be a hex color, and you can change the color's opacity easily, instead of the rgba (rgba(48, 3, 252, 0.902), rgba(153, 7, 250, 0.902)), It can be short to (#3204fde6, #9907fae6)

header {
  height: 100vh;
  width: 100%;
  color: white;
  font: bold 6.5em/2em monospace;
  display: flex;
  justify-content: center;
  align-items: center;
  
  background: linear-gradient(to top, #3204fdba, #9907facc), url(https://picsum.photos/1280/853/?random=1) no-repeat top center;
}

<header>Hello World</header>

See here CodePen

You may use negative superthick semi-transparent border...

.red {
    outline: 100px solid rgba(255, 0, 0, 0.5) !important;
    outline-offset: -100px;
    overflow: hidden;
    position: relative;
    height: 200px;
    width: 200px;
}

<div class="red">Anything can be red.</div>
<h1>Or even image...</h1>
<img src="https://cdn.sstatic.net/Sites/stackoverflow/company/img/logos/so/so-logo.png?v=9c558ec15d8a" class="red"/>

This solution requires you to know exact sizes of covered object.

You could use the hue-rotate function in the filter property. It's quite an obscure measurement though, you'd need to know how many degrees round the colour wheel you need to move in order to arrive at your desired hue, for example:

header {
    filter: hue-rotate(90deg);
}

Once you'd found the correct hue, you could combine the brightness and either grayscale or saturate functions to find the correct shade, for example:

header {
    filter: hue-rotate(90deg) brightness(10%) grayscale(10%);
}

The filter property has a vendor prefix in Webkit, so the final code would be:

header {
  -webkit-filter: hue-rotate(90deg) brightness(10%) grayscale(10%);
          filter: hue-rotate(90deg) brightness(10%) grayscale(10%);
}

#header.overlay {
    background-color: SlateGray;
    position:relative;
    width: 100%;
    height: 100%;
    opacity: 0.20;
    -moz-opacity: 20%;
    -webkit-opacity: 20%;
    z-index: 2;
}

Something like this. Just add the overlay class to the header, obviously.

Here's a creative idea using box-shadow:

#header {
    background-image: url("apple.jpg");
    box-shadow: inset 0 0 99999px rgba(0, 120, 255, 0.5);
}

What's happening

1. The background sets the background for your element.

2. The box-shadow is the important bit. It basically sets a really big shadow on the inside of the element, on top of the background, that is semi-transparent

Use mutple backgorund on the element, and use a linear-gradient as your color overlay by declaring both start and end color-stops as the same value.

Note that layers in a multi-background declaration are read much like they are rendered, top-to-bottom, so put your overlay first, then your bg image:

#header {
  background: 
    linear-gradient(to bottom, rgba(100, 100, 0, 0.5), rgba(100, 100, 0, 0.5)),
    url(../img/bg.jpg) 0 0 no-repeat fixed;
  height: 100%;
  overflow: hidden;
  color: #FFFFFF
}

To add an overlay, you can use the CSS background-blend-mode property something like this:

#header {
  background: url("img/image.jpg") 0 0 no-repeat fixed;
  height: 100%;
  overflow: hidden;
  background-color: hsl(206, 27%, 38%);
  background-blend-mode: multiply;
}

You can also add an additional class with such settings. Overlay will not overlap content and no additional tag is needed

.overlay {
  position: relative;
  z-index: 0;
}

.overlay::after {
    content: '';
    position: absolute;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
    background: red;
    opacity: .6;
    /* !!! */
    z-index: -1;
}

https://codepen.io/zeroox003/pen/yLYbpOB

If you don't mind using absolute positioning, you can position your background image, and then add an overlay using opacity.

div {
    width:50px;
    height:50px;
    background:   url('http://images1.wikia.nocookie.net/__cb20120626155442/adventuretimewithfinnandjake/images/6/67/Link.gif');
    position:absolute;
    left:0;
    top:0;
}

.overlay {
   background:red;
   opacity:.5;
}

See here: http://jsfiddle.net/4yh9L/

In helpshift, they used the class home-page as

HTML

<div class="page home-page">...</div>

CSS

.home-page {
    background: transparent url("../images/backgrounds/image-overlay.png") repeat 0 0;
    background: rgba(39,62,84,0.82);
    overflow: hidden;
    height: 100%;
    z-index: 2;
}

you can try similar like this

If you want to just add a class to add the overlay:

span {
  padding: 5px;
}

.green {
  background-color: green;
  color: #FFF;
}

.overlayed {
  position: relative;
}

.overlayed::before {
  content: ' ';
  z-index: 1;
  position: absolute;
  top: 0;
  bottom: 0;
  left: 0;
  right: 0;
  background-color: #00000080;
}

.stand-out {
  position: relative;
  z-index: 2;
}

<span class="green overlayed">with overlay</span>
<span class="green">without overlay</span>
<br>
<br>
<span class="green overlayed">
  <span class="stand-out">I stand out</span>
</span>

Important: the element you put the overlayed class on needs to have a position set. If it doesn't, the ::before element will take the size of some other parent element. In my example I've set the position to "relative" via the .overlayed rule, but in your use case you might need "absolute" or some other value.

Also, make sure that the z-index of the overlayed class is higher than the ones of the eventual child elements of the container, unless you actually want for those to "stand out" and not be overlayed (as with the span with the stand-out class, in my snippet).