Simply click on the tear off button of the local chat (the button next to the "X" close button), and it will merge the local chat and the IM floaters.
And if you want the chat input line in the local chat history (v1.23.5's style), open the Preferences floater and in the "Cool features" tab, "User Interface" sub-tab, uncheck "Use the old chat history window" and finally restart the viewer.