background-image
takes multiple values.
so a combination of just 1 color linear-gradient and css blend modes
will do the trick.
.testclass {
background-image: url("../images/image.jpg"), linear-gradient(rgba(0,0,0,0.5),rgba(0,0,0,0.5));
background-blend-mode: overlay;
}
note that there is no support on IE/Edge for CSS blend-modes at all.