This might not come as a surprise to anyone but when I found this out I thought it was so cool.

If you apply a

filter: drop-shadow(PIXELVALUE PIXELVALUE PIXELVALUE COLOR);

style to a .PNG image with an alpha channel then it will render the drop-shadow on the actual image rather than a box around its border. You can see this in the following example:

filter: drop-shadow(55px 0px 10px black);