let marker = document.querySelector('#marker');
let list = document.querySelectorAll('ul li');

function moveIndicator(e){
  marker.style.left = e.offsetLeft+'px';
  marker.style.width = e.offsetWidth+'px';
}
list.forEach(link => {
  link.addEventListener('mousemove', (e) => {
    moveIndicator(e.target);
  })
})

function activeLink(){
  list.forEach((item) => 
  item.classList.remove('active'));
  this.classList.add('active');
}
list.forEach((item) => 
item.addEventListener('mouseover', activeLink));