Scroll to top

index.html

<a class="scroll-to-btn" id="scrollToTopBtn">наверх ↑</a>

Scroll to top js

/* scroll to top */
var scrollToTopBtn = document.getElementById("scrollToTopBtn");
var rootElement = document.documentElement;

function scrollToTop() {
  // Scroll to top logic
  rootElement.scrollTo({
    top: 0,
    behavior: "smooth"
  })
};
scrollToTopBtn.addEventListener("click", scrollToTop);

style.css

html {
    scroll-behavior: smooth;
}