Hello Dipscom,
I am really grateful for your answer and your help. I really am a beginner in this thing so I probably will start from the basic. I already have gone through the basic for GSAP and looked into the forum but I still could not find any topic regarding the background animation in that particular website. I just thought maybe they used some software like Adobe Animate CC or something like that so I know where to start learning. But anyway, I am really grateful for your answer and thank you.