Роман

const blocks = document.querySelectorAll('.block');

const scrollTo = (delta) => {
  for (let i = 0; i < blocks.length; i++) {
    const elem = blocks[i];
    elem.classList.remove('active');
    if (i == delta) {
      elem.classList.add('active');
    }
  }
}
let step = 0;
document.addEventListener('wheel', (e) => {
  if (e.deltaY < 0) {
    step -= 1;
    if (step <= 0) { step = 0}
  }
  if (e.deltaY > 0) {
    step += 1;
    if (step >= 5) { step = 4 }
  }
  console.log(step);
  scrollTo(step);
});