Geb functional testing of text-transform

I'm trying to test a requirement that says the first name field is always capitalized. I have an input field that looks like the following:

<input type="text" class="form-control" id="firstName" name="firstName" style="text-transform: capitalize" />

In my Geb test, my current testing code looks like this:

def "First Name field automatically capitalizes first letter"() {
    given:
    def page = to NewRegisterPage

    when:
    page.containers.firstName << 'mary'

    then:
    page.containers.firstName.value() == 'Mary'
}

However, this always fails. I'm wondering if there is a way to validate that the text-transform has taken place. I am currently using both the PhantomJS driver and the Chrome driver.