I have noticed that you can create grid-lines by using, for example:
background-image: repeating-linear-gradient(0deg,transparent,#CCC 0,transparent 3px,transparent 10%), repeating-linear-gradient(-90deg,transparent,#CCC 0,transparent 3px,transparent 10%);}
So, my question is how can you create grid-lines that will go on top of an background image while not using the above?