庭

How it works

が (subject) points out the subject (庭(にわ) (garden)), and きれい (pretty) describes it. きれい (pretty) is a な-adjective, but here it sits at the very end as the predicate, so it needs no noun after it. There's no copula at all — in plain, casual speech the だ (is) you might expect is simply dropped, leaving a relaxed “the garden, pretty”.