Control Add-In in Business Central

Hello, Im an intership student and i really could use some help, im trying to implement a timeline with javascript in business central but im not able to make business central to recognize the mouseover, where do i have to put the javascript in order to do that?
the javascript im trying to implement: https://codepen.io/meric-fournier/pen/WGOLXb

i created the usercontrol but i dont whal ese i have to do
thanks in advance