smooth-scroll.css

@keyframes smoothscroll1 {
  from,
  to {
    scroll-behavior: smooth;
  }
}

@keyframes smoothscroll2 {
  from,
  to {
    scroll-behavior: smooth;
  }
}

html {
  animation: smoothscroll1 1s;
}

html:focus-within {
  animation-name: smoothscroll2;
  scroll-behavior: smooth;
}