const translate = document.querySelectorAll(".translate");
const bigTitle = document.querySelector(".bigTitle");
const header = document.querySelector("header");
const section = document.querySelector("section");

let header_height = header.offsetHeight;
let section_height = section.offsetHeight;

window.addEventListener('scroll', () => {
    let scroll = window.pageYOffset;
    let sectionY = section.getBoundingClientRect();
    
    translate.forEach(element => {
        let speed = element.dataset.speed;
        element.style.transform = `translateY(${scroll * speed}px)`;
    });

    bigTitle.style.opacity = - scroll / (header_height / 2) + 1;
});

let mybutton = document.getElementById("btn-back-to-top");

window.onscroll = function () {
  scrollFunction();
};

function scrollFunction() {
  if (
    document.body.scrollTop > 20 ||
    document.documentElement.scrollTop > 20
  ) {
    mybutton.style.display = "block";
  } else {
    mybutton.style.display = "none";
  }
}

mybutton.addEventListener("click", backToTop);

function backToTop() {
  document.body.scrollTop = 0;
  document.documentElement.scrollTop = 0;
}