Althought it seems not work for me(at least not as I expect), thanks again.
It is quite hard to find these two lines without you instruction.
Anyway I have changed my mind not to directly edit cinnamon.css for menu interface editing,maybe install a new applet like "starkMenu" is more easier to newbies.
Tweaking the appearance is somehow always the first step for newbies to get better understanding of using Linux(and more fun/achievement).
Sometime just get used to it is another way! For me now, these spaces are good for my eyes...