As far as I can tell from the page-object gem code, I do not believe that the page-object gem supports :css locators for watir-webdriver. At least it is not included in the watir_finders method - see element.rb and div.rb. I am guessing that the reason is due to watir-webdriver's current limitation that :css locators can only be used when using the element
method - see watir-webdriver's issue 124.
Solution 1 - Use a Block
However, you could workaround these issues by defining the div in your page object with a block.
Assuming the html:
<div class="active" style='display: block;'>text</div>
The following worked for me:
div(:select){ browser.element(:css => 'div.active[style="display: block;"]') }
Solution 2 - Use Xpath
Alternatively, you could convert your css locator to an xpath locator:
div(:select2, :xpath => '//div[@class="active" and @style="display: block;"]')
Note that if you go this way, you might want to look at this other question, which talks about using a more robust locator for the class.