Look at the area circled in red. The circlular stone tile normally overlaps the grass with an ugly border (like the one circled in blue). How did the maker of this make it so that the tile didn't overlap, but instead came together neatly?
In Advanced - custom tileset, you can "move tile left" and "move tile right." When two tiles are placed next to each other, the one that is further to the right in the tileset will "hang over" the one that is farther left.
