The other two are the pros, I am somewhat of an officious dabbler. I know enough to be dangerous.

The term "text box" is used in a couple of ways in Word jargon, much to the confusion of all. The type we are talking about is found under Insert > Text Box.
It is a graphic element or shape and can be resized/rotated.
You can have it with or without borders.

When you are inside a text box a special contextual tab should appear in the Ribbon that you can use to make changes. It is the Shape Formatting Tab and has the same controls as the Drawing Formatting Tab
I would suggest light-gray shading and no borders.