Best solution I found to make the background image in a div slightly transparent/opaque without impacting content of the div:
background: linear-gradient( rgba(255, 255, 255, 0.8), rgba(255, 255, 255, 0.8) ), url('../img/image.png');
background-repeat: no-repeat;
background-position: center;
➤ change 255 to 0 for black opacity.