First, select Add New... in the context menu of the tictactoe project and choose to create a new Qt Designer Form Class, as shown in the following screenshot:
In the window that appears, choose Dialog with Buttons Bottom:
Adjust the class name to ConfigurationDialog, leave the rest of the settings at their default values, and complete the wizard. The files that appear in the project (.cpp, .h, and .ui) are very similar to the files generated for the MainWindow class when we created our ...