Where the name “+ or -” stands more for “positive or negative” than for “more or less”: two square rings overlap on one side, but one is, precisely, the opposite of the other. The same goes for the two central spaces framed by the rings.
Once inside, it is possible to walk this transition from positive to negative (where no one can tell which is one and which is the other) from closed to open, from light to shadow, seamlessly, endlessly. But because nuances are important, it will always be possible, through small holes, that from one you can have a glimpse of the other, and the two terms to blend in the middle of the path.