TweetDeck did an update, with more features, a cleaner design and support for polls and GIFs. The composition window works well no matter what theme you choose. Users are treated to an upgraded window with options for creating a poll, adding GIFs to tweets, a new emoji picker, and tagging and image descriptions.
Currently, Twitter is not forcing the new update to users. Those who liked the old can currently use the original interface. While it's more convenient, there are some warnings that TweetDeck users have to deal with, including extra clicks to come between multiple TweetDeck accounts and more notably. They cannot schedule tweets in advance.
Twitter puts the new features on the server's side so you don't have to download a new version to see the changes. TweetDeck for Mac is a free app that can be downloaded for free on the Mac App Store.