Creating vertical drop downs in wordpress

I'm trying to change the navigation on the left side bar to have the "children" not visible until the user is clicked on the parent page, or until the main item has been rolled over. Can I do this with CSS?

The link:

The Css:

#content div.column-content {font-size: 14px; line-height: 20px; }
#content {border-bottom: solid 1px #ccc; margin-bottom: 15px; }
#content li {font-size: 11px; font-weight: bold; padding: 5px 0;}
#content li a {color:#666; }

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