const start = document.querySelector('#modalReg-start');
const end = document.querySelector('#modalReg-end');
const modalWindow = document.querySelector(".modalRegisterNow");
document.addEventListener("scroll", ()=>{
    start.getBoundingClientRect().top;
    if(start.getBoundingClientRect().top < 0){
        if(!modalWindow.classList.contains("visible")){
            modalWindow.classList.add("visible")
        }
        if(end.getBoundingClientRect().top < 0){
            if(modalWindow.classList.contains("visible")){
                modalWindow.classList.remove("visible")
            }
        }
    }
    else {
        if(modalWindow.classList.contains("visible")){
            modalWindow.classList.remove("visible")
        }
    }
})