step one:
draw a Circle dont worry about the fill just yet

step two:
delete the outline of the circle and change the fill to radial

step three:
on the color tab change both of the gradient fills to #00000

step four:
change the alpha of the left gradient color to 50% and the right to 0%

you should now have a circle that looks like this:

step five:
shrink it down to an oval shape

step six: convert it to a symbol with an apropriate name (such as green_stick_shdow)

finally place the shadows on the bottem layer (unless there is a background) play around with the positioning of the shadows and remember these factors ~ direction of light and distance from floor.

for use on a colored background, copy the same color codes as the floor, and make it a bit darker and put them in place of #00000
here is an example

