Hi there and welcome
This is the new outlook that they are slowly rolling out. You have been randomly picked my microsoft to trial this, and there is way to avoid this as Microsoft dictate it, but all users will be on this soon.
You can see an overview of it here
and if you have any specific questions about it, please do not hesitate to let me know.
If you would like any additional information or assistance, please do not hesitate to let me know.
Else if you can take a second to rate my service by clicking one of the stars at the top of the screen then submit, that would be greatly appreciated.