anchor-menu.css

.anchor-menu {
  background-color: rgba(255, 255, 255, 0);
  position: fixed;
  bottom: 0;
  left: 0;
  z-index: 1000;
  font-family: 'Roboto';
  font-size: 14px;
  width: 20px;
  transition: all 0.3s ease;
  white-space: nowrap;
  border-radius: 5px 10px 10px 5px;
}

.anchor-menu ul {
  list-style: none;
  padding: 0.2rem 0.5rem 0.2rem 0;
  margin: 0;
}

.anchor-menu li {
  position: relative;
  cursor: pointer;
}

.anchor-menu li:hover {
  font-weight: bold;
}

.anchor-menu span {
  padding-left: 0.5rem;
  display: inline-block;
  transform: translateX(-100%);
  transition: all 0.3s ease;
}

.anchor-menu li::after {
  content: '';
  background-color: #747474;
  display: block;
  width: 1rem;
  height: 3px;
  position: absolute;
  top: 50%;
  transition: all 0.3s ease 0.3s;
}

.anchor-menu li.active {
  color: #2176ff;
  font-weight: bold;
}

.anchor-menu li.active::after {
  background-color: #2176ff;
  width: 2rem;
}

.anchor-menu:hover {
  width: 150px;
  transition: all 0.3s ease 0.3s;
  background-color: rgba(255, 255, 255, 0.7);
}

.anchor-menu:hover span {
  transform: translateX(0%);
  transition: transform 0.3s ease 0.3s;
}

.anchor-menu:hover li::after {
  transform: translateX(-100%);
  transition: all 0.3s ease;
}

@media only screen and (max-width: 900px) {
  .anchor-menu {
    display: none;
  }
}

anchor-menu.js

var $ = jQuery
$(document).ready(function(){
  var sections = $('h1, h2').map(function(){
     return {
       title: $(this).text(),
       el: $(this)
     }
  }).get()
  if(sections[0].title !== 'aetherAI') return
  var body = $('html, body')
  var anchorContent = '<ul>' + sections.map(function(section){return '<li><span>' + section.title + '</span></li>'}).join('') + '</ul>'

  $('<div class="anchor-menu"/>').appendTo('body').html(anchorContent)
  sections.forEach(function(section){
    section.position = section.el.offset().top
  })
  $(document).on('click', '.anchor-menu li', function(){
    var sectionIndex = $(this).index()
    var position = sectionIndex === 0 ? 0 : sections[sectionIndex].el.offset().top - 32
    body.stop().animate({scrollTop: position}, 500, 'swing')
  })
  $(document).scroll(function(){
    var centerLine = body.scrollTop() + $(window).height() / 2
    var found = false;
    for(var i = 0; i < sections.length; i++) {
      var section = sections[i]
      if(section.el.offset().top > centerLine) {
        $('.anchor-menu li').eq(i - 1).addClass('active').siblings('.active').removeClass('active')
        found = true;
        break;
      }
    }
    if(!found) {
      $('.anchor-menu li').eq(sections.length - 1).addClass('active').siblings('.active').removeClass('active')
    }
  }).scroll()
})