The Office team didn't only make a good use of the Ribbon, TextBox or the TextBlock codes. Instead their team created the UI themself, which means that they didn't just stick to the default (built-in) controls provided by the .NET developers for the WPF framework. You can stylize the objects, or you can create your own objects which inherit from these base-classes to expose similar functions and raise the same events in the application context.
Ribbon, TextBox and such similar controls are provided for developers, to think and focus on the business-logic layer and not how to create the GUI for the application. If you also have to customize the GUI, you can create your own custom objects, which would inherit from these base-classes for the GUI; such as TextBox, Button, TextBlock and Ribbon. Office team, started off with removing the Window styles, and then created everything (including the buttons to minimize or close the application) themself. For example, have a look at
this[
^] property of Window class, you can set it to none and there won't be any default border or button from the Window. But you would have to create them yourself,
GitHub[
^] also makes use of the same framework and the methodology. You can take the GitHub application as an example for this process, and then continue sharpening the application to add a few more features to it.