Overflow-y scroll question

I have the overflow-y:scroll option for a div with text. However, the scroll "space" (for lack of a better word for it) appears whether the text requires scrolling or n开发者_StackOverflow社区ot. How do I make the appearance of the scroll "space" conditional on whether the text has a long enough height?

Change scroll to auto

This value is browser and media dependent, but should allow for a vertical scrollbar if possible in case of overflow.

http://www.css3.com/css-overflow-y/

scroll means to always show the scrollbar; auto means to show it when necessary. Change it to auto instead.