今日

How it works

は (topic) sets 今日(きょう) (today) as the topic — “as for today…”. The feeling word 楽しい(たのしい) (fun) is an i-adjective, so its own ending changes to make the past tense: 楽しかった(たのしかった) (was fun). No です (is) is needed — the adjective itself carries the tense, and the plain form keeps it casual.