How do you prevent a user from changing the size of a program form when C # develops a WinForm form program?

When you use C # to develop a WinForm form program, you are prohibited from changing the size of the program form:

At development time, sometimes we set the background of the form, and when we change the size of the form, the window is not full of background images,

There is a part of the blank, which is a bit unattractive, to the form program at run time without the user to change the size of the window, we can

The FormBorderStyle value in the form's properties is set to FixedSingle or FIXED3D, and the window size cannot be changed.

When the form is maximized, it also exposes the problem above, so we're going to remove the function that maximizes the form,

That is, set the value of MaximizeBox to False