You have destroyed OneNote 2016 with this search bar change. This is likely the dumbest decision I've ever seen a UX designer make EVER. It LITERALLY covers the contents of the page you are searching for, WHO THOUGHT THIS WAS A GOOD IDEA???
Please, for all that is good in the world, LEAVE ONENOTE 2016 ALONE! It was perfect, it doesn't need stupid UX changes just for the sake of change. Move the search bar back, or make it optional. I'm now going to have to rollback my entire Office update and block updates because of this god awful change.
I use OneNote for BUSINESS, and this change has destroyed my ability to actually do real work!!! If you are going to ruin a version of OneNote, ruin the "modern" version. Leave the version with a working search and offline notes function ALONE.