yo first you need to contact the support for css acess; after you go to your page and edit theme;; go to custom css and you paste this
.buy_btn:hover{
box-shadow: 0px 0px 0px 4px #FFF;
border-radius: 1%;
}
.buy_btn{
animation:boxanim 1.5s linear infinite
}
there some tutorials on youtube here's one