Add a grass sprite and a treasure chest

I added the grass to experiment with sprites using CSS. As the entire grass area is a single div, I had to create another absolute div that is full width and full height of the grass container. Then I run a loop and insert 2500 div that has a css background of the sprites.

After which made some adjustment to the z-index to ensure the treasure chest can appear at the top.

I think it's not looking too bad. I'm just hoping I'm able to find other sprites that would match with this current tile.