css background image black overlay
<style>
#wrapper{
position:relative;
width:fit-content;
height:fit-content;
}
#overlay{
position:absolute;
top:0;
width:100%;
height:100%;
z-index:1;
background-color:black;
opacity:.5;
}
</style>
<div id='wrapper'>
<img src="https://hips.hearstapps.com/hmg-prod.s3.amazonaws.com/images/dog-puppy-on-garden-royalty-free-image-1586966191.jpg?crop=1.00xw:0.669xh;0,0.190xh&resize=640:*" alt="">
<div id='overlay'></div>
</div>