How to Set The Opacity Of Body Background Image in CSS, HTML

Question

how can I set or change the body background image opacity without affecting the content or you can say to keep the focus on the content and making the background more dark?
I tried this in in CSS
body {
background-image;url("img url")
opacity: 0.5;
}
but it changed the opacity of whole page including the content.

Answer 1

thanks, I've understood.

Answer 2

div{
background-image:url("https://static.pexels.com/photos/20974/pexels-photo.jpg");
opacity:0.5;
position:absolute;
top:0;
bottom:0;
right:0;
left:0;
background-repeat: no-repeat;
background-size: cover;
z-index:-1;
}

Answer 3

https://code.sololearn.com/W2fzI2WhflM6/?ref=app

zindex is key to success

other elements shouldn't wrap inside your image tag otherwise will effects by opacity