Combat log separate from chat log

I just pulled my combat log tab out into a separate chat window on accident, I don't want it that way. Previously, if i recall correctly, all you had to do was drag the new window back into your chat log and itd become a tab again.

I assume this is because of the new chat changes and all, but I'm not sure because I haven't done this in a pretty long time. How do I join the two windows into one with tabs again?