You need to go to Appearance > Customize > Front Page sections > Service Section and there should be a background tab that allows you to add a new background.
For contact 7, you can use the following plugin to change the background:
I know about the background but I need to use the Project Section Background ( the Default Background ) in mentioned Sections ( Service , Team , Contact ).
I want to use the Thin Line Background used by default on Project Section.
How can I make it or how can I insert the Project Section Default Background?