Help with styling twenty eleven theme in Word Press

This site could be a real saviour, can't believe I haven't found it before!

I am trying to edit the style sheet in twenty eleven in WP to get the menu to do something specific.

I am at the very beginning so there is no content, and the actual style isn't even set - I'm just trying to get my head around things.

The site is here.

Ok at the moment on the active page, the menu has the image with the black and white checking on it - this I was able to work out pretty easily and the styling is:

#access .current_page_item > a {
 
background-image: url(images/active2.png);
background-repeat: no-repeat;
 
font-weight: bold;
	color: #FF0000;
 
}

The problem I have, is in the sub-menu I want the active page to be an image with only 1 column of checks, (active3.png). The existing style sheet uses the above current page item right down the menu.

I tried to create a new section:

#access .current_page_item > ul a {
 
background-image: url(images/active3.png);
background-repeat: no-repeat;
 
	font-weight: bold;
	color: #CC33CC;
 
}

(The colours are irrelevant it is just my way of tracking which code applies where. Anyway this style isn't being picked up.

I suspect I'm not understanding the structure properly.

Your advice would be appreciated.