We're starting to sneak in a little more CSS that you haven't seen yet. Don't worry about this for now; we just want things to look a little bit prettier, and this CSS will not interfere with your task.
For this one you will probably need to edit the HTML a little bit. Often with flexbox you need to add containers around things to make them go where you need them to go. In this case, you probably want to separate the items that go on the left and right of the header.