You cannot change the opacity of a background-image
with CSS. However, there are ways of achieving the same result.
This method uses the :after pseudo class which is absolutely positioned inside its parent. The background image is set on this pseudo element along with the opacity giving the impression that the background opacity is set on the background itself.
HTML
<div>
Text on top, no big deal, no big deal. Just a little text and stuff. That's all.
</div>
CSS
div {
width:320px;
height:374px;
display: block;
position: relative;
border: solid 1px #f00;
}
div::after {
content: "";
background-image: url('http://placehold.it/800x600');
background-size: cover;
background-repeat: no-repeat;
opacity: 0.5;
top: 0;
left: 0;
bottom: 0;
right: 0;
position: absolute;
z-index: -1;
}
If you need backwards compatibility, you will need an extra element in your markup to achieve the same result:
HTML
<div class="container">
<div class="background"></div>
Text on top, no big deal, no big deal. Just a little text and stuff. That's all.
</div>
CSS
.container {
width:320px;
height:374px;
display: block;
position: relative;
border: solid 1px #f00;
}
.container .background {
content: "";
background-image: url('http://placehold.it/800x600');
background-size: cover;
background-repeat: no-repeat;
opacity: 0.5;
top: 0;
left: 0;
bottom: 0;
right: 0;
position: absolute;
z-index: -1;
}
Here is a great article with a CSS3 method of achieving the same result:
http://css-tricks.com/snippets/css/transparent-background-images/