If you're looking to add some interactivity to your website, consider using the powerful :hover
CSS selector (http://www.example.com/CSS-hovers). Another option is to include a title
attribute on links for creating handy tooltips.
LATEST UPDATE:
After reading through your feedback, it seems like you're interested in replicating the "Page Indicator" found at the bottom right of the reference website.
To achieve this effect, simply tweak the CSS of the targeted indicator when switching active divs. Check out this straightforward example: http://jsfiddle.net/123abc/3/
Keep in mind that if you're open to utilizing jQuery or a similar library, handling animations, class toggling, and other functionalities needed to imitate this feature become much more streamlined.