Thank you very much Cassie, I will follow the guidline forum in the future, sorry.
First, how do I make the ball deform when moving the mouse ?
Second, how do I make the border of the red section bounce when the cursor enters above it ?
Here's a codepen that I adjusted :
https://codepen.io/DinhoDev/pen/zYdqaQG
Thank you in advance for your answer. ?