Hi Susie:
Not a silly question I dont have that much experiance with the css3 box shadows,
but i think i can help out with the CSS shorthand commands and there values.
4 values=top,right,bottom,left
3 values=top,(right and left),bottom
2 values=(top and bottom) (right and left)
1 value=top,bottom,(right and left)
hope that helps.