How to darken a background using CSS?

I have an element with text in it. Whenever I decrease the opacity, then I decrease the opacity of the WHOLE body. Is there any way I can just make the background-image darker, and not everything else?

background-image:url('http://fc02.deviantart.net/fs71/i/2011/274/6/f/ocean__sky__stars__and_you_by_muddymelly-d4bg1ub.png');

Solution

Just add this code to your image css

 body{
 background:
        /* top, transparent black, faked with gradient */ 
        linear-gradient(
          rgba(0, 0, 0, 0.7), 
          rgba(0, 0, 0, 0.7)
        ),
        /* bottom, image */
        url(https://images.unsplash.com/photo-1614030424754-24d0eebd46b2);
    }

Reference: linear-gradient() - CSS | MDN

UPDATE: Not all browsers support RGBa, so you should have a 'fallback color'. This color will be most likely be solid (fully opaque) ex:background:rgb(96, 96, 96). Refer to this blog for RGBa browser support.

UPDATE 2023: All modern browsers now supports RGBa : caniuse link