Beginner, there is a need to open Spring Boot the demo with Idea. I chose to import (Import Project Options) file, such as title errors and yml file format does not display properly (leaves).
Directory look back, found a main.iml file (FIG resources on below), the file is not the original folder. After you remove the iml file, all back to normal
And teachers discussed later, you can open (open option) files directly, such errors do not occur.