You could select and style this with JavaScript or jQuery, but CSS alone can't do this.
For example, if you have jQuery implemented on the site, you could just do:
var last_visible_element = $('div:visible:last');
Although hopefully you'll have a class/ID wrapped around the divs you're selecting, in which case your code would look like:
var last_visible_element = $('#some-wrapper div:visible:last');