Welcome to CodeProject !
Note: the "Bunifu UI" you refer to is a commercial collection of .NET controls with obviously advanced graphic features; it has many competitors like DotNetBar, Telerik, Lidor Suite, etc. My comments here are about the general aspects of learning C#, and the .NET Framework.
Using any of these powerful collections of controls will require you to learn the syntax for their API's ... which may, or may not, be consistent with the API's of the built-in Microsoft controls (which are also inconsistent in many ways, LOL). I suggest that new learners put their energy into learning the basics of the .NET FrameWork, Platform (Win Forms, WPF, ASP.X), and C# language, first.
Challenging yourself to create a UI like something you've seen, and like, is a very good way to develop your language and framework knowledge and skills.
However, imho, it's very important at the beginning
of your journey towards technical competency and mastery, to get a solid understanding of the language you are using, and how it is embedded in the series libraries that make up the .NET Framework.
Of course, CodeProject itself is a wonderful resource for studying every aspect of C# and the .NET framework. There are great tutorials, in-depth articles on programming areas from algorithms to data structures to UI, and, of course, examples of custom controls, and other practical projects that are immediately useful.
There are excellent books on C#: my favorite intro book authors are Jesse Liberty, and Matthew MacDonald ... those are not free. For free, I suggest you get one, or both, these free books:
Charles Petzold : ".NET Book Zero" : [^
Svetlin Nakov, Veselin Kolev, and others : "Fundamentals of Computer Programming with C#" : [^
Important choices to make are whether to use Windows Forms, or WPF, or some web-centric flavor of ASP.NET.
WPF provides built-in animation features, and advanced graphics (vector drawing, gradients, etc.). imho, it has a steep initial learning curve.
Windows Forms provides a very stable and consistent foundation, and, imho, is relatively easy to get going in. Simple animation is easy to do.
Now: let's get to work :)