Transparent background with body::after limited by the screen size - html

Question

I've been using that code on my body, to get a full background with some mi-transparent white background on it :
body {
background: url('../images/bg.jpg') no-repeat center center fixed;
padding-top: 50px;
}
body::after {
content: "";
background: white;
opacity: 0.5;
top: 0;
left: 0;
bottom: 0;
right: 0;
position: absolute;
z-index: -1;
}
The problem is that the white background doesn't go lower than the screen size as you can see here. Any idea how to fix that ?

Answer 1

It's because body::after isn't fixed, change the css like this :
body::after {
content: "";
background: white;
opacity: 0.5;
top: 0;
left: 0;
bottom: 0;
right: 0;
position: fixed;
z-index: -1;
}
Here is an example with a black background

Answer 2

Instead of using a ::before or ::after pseudo element, you can use css multple backgrounds.
Generate the base64 from this site: http://px64.net/
Apply the background to the body element.
#foo {
width: 400px;
height: 150px;
visibility: visible;
}
#foo {
background: url(data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAAEAAAABCAYAAAAfFcSJAAAADUlEQVR42mNgYPhfDwACggF/yWU3jgAAAABJRU5ErkJggg==) repeat, url(http://www.openkorat.com/wp-content/uploads/2015/08/extra-bg-green.jpg) no-repeat;
background-size: auto, cover;
}
<div id="foo"></div>

Answer 3

Make the ::after element position: fixed.
Fiddle
body {
background: url('../images/bg.jpg') no-repeat center center fixed;
padding-top: 50px;
}
body::after {
content: "";
background: red;
opacity: 0.5;
top: 0;
left: 0;
bottom: 0;
right: 0;
position: fixed;
z-index: -1;
}
div {
height: 800px;
}
<div>div</div>