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HTML 

              
                <div class='phone'>
  <div class='inside'>
    <div id='title-page' class=''>
      <h1>A Story</h1>
      <h3>as told by a few letters</h3>
      <div class='next' style='display:block;'><a href='#ch1'>&#x2193;</a></div> 
    </div>
    
    <div id='ch1' class='page'>
      <div class='ch1-block'>
        <p>There once was a little 'a'.<br><br> Alone they sat dreaming of one day becoming a big 'a'.</p>
       <div class='ch1-game'>
         <h1 onclick='changeFont(this)'>a</h1>
        </div> 
      </div>
      <div class='next'><a href='#ch2' onclick='ch2Open()'>&#x2193;</a></div>
    </div>
    
     <div id='ch2' class='page'>
      <div class='ch1-block'>
       <div class='ch2-game'>
         <h1 onclick='ch2(this)'>a</h1>
         <h1 class='b'>b</h1>
         <p>Because I can. Now leave me little 'b'.</p>
        </div> 
      </div>
      <div class='next'><a href='#ch3' onclick='ch3Open()'>&#x2193;</a></div>
    </div>
  
  <div id='ch3' class='page'>
      <div class='ch1-block'>     
       <div class='ch3-game'>
         <h1 onclick='ch3(this)'>a</h1>
         <h1 class='c'>c</h1>
         <p>I guess I am a big 'A'.</p>
        </div> 
      </div>
      <div class='next'><a href='#title-page' onclick='theEnd()'>&#x2193;</a></div>
    </div>
  </div>
</div>

<link href="https://fonts.googleapis.com/css?family=Montserrat:300,500,700,900&display=swap" rel="stylesheet">
!

CSS 

              
                ::-webkit-scrollbar {
  width:5px;
}
:root {
  --fontFamily:'Montserrat', sans-serif;
  --hide:none;
  --aAnimation:ch1 2s linear infinite;
  --bAnimation:none;
  --bBubble:"Why do you daydream little 'a'?";
  --cAnimation:none;
  --cBubble:"Whatcha doing little 'a'?"
  
}

html {
  font-family: 'Montserrat', sans-serif;
  scroll-behavior: smooth;
  background:linear-gradient(to bottom right, transparent 18px, #efefef 18px, transparent 20px);
  background-size:20px 20px;
}

.phone {
  width:330px;
  height:668px;
  border-radius:20px;
  box-shadow:0 0 0 2px lightgray;
  position:absolute;
  top:50%;
  left:50%;
  transform:translate(-50%,-50%);
  background:white;
}
.inside {
  width:320px;
  height:568px;
  box-shadow:0 0 0 2px lightgray;
  position:absolute;
  top:50%;
  left:50%;
  transform:translate(-50%,-50%);
  overflow:hidden;
  scroll-behavior: smooth;
  background:white;
}

#title-page {
  width:100%;
  min-height:568px;
}

#title-page h1 {
  font-size:85px;
  line-height:100%;
  font-weight:900;
  padding:0 20px;
  text-align:left;
}
#title-page h3 {
  padding:0 20px;
}

.next {
  position: absolute;
  bottom: 10px;
  right: 5px;
  font-size: 36px;
  line-height: 100%;
  user-select:none;
  display:none;
  animation:downArrow 2s linear infinite;
}
@keyframes downArrow {
  50% { bottom:0px; }
}
.next a{  
  color:black;
  text-decoration:none;
}

#title-page .next {
  right:50%;
  transform:translateX(50%);
}
/* ch1 */
.page {
  margin-top:100px;
  position:relative;
}
.ch1-block {
  width:100%;
  height:568px;
  background:#efefef;
}

.page p {
  padding:20px;
  position:absolute;
  bottom:0;
}

.ch1-game {
  position:absolute;
  bottom:0;
  width:100%;
  height:50%;
}
.page h1 {
  font-size:100px;
  font-weight:300;
  text-align:center;
  margin-top:0;
  user-select:none;
  cursor:pointer;
  animation:var(--aAnimation);
}
@keyframes ch1 {
  50% { transform:scale(1.2) }
}
.ch1-game h1:before {
  content: '';
  position: absolute;
  top: -32%;
  left: 50%;
  transform: translateX(-50%);
  width: 30px;
  height: 120px;
  background: red;
  background: radial-gradient(circle, white 50%, transparent 50%);
  background-size: 30px 30px;
  display:var(--hide);
}
.ch1-game h1:after {
  content: 'A';
  position: absolute;
  top: -75%;
  left: 50%;
  transform: translateX(-50%);
  font-size: 72px;
  width:115px;
  height:115px;
  line-height: 115px;
  font-weight: 700;
  font-family: var(--fontFamily);
  background: white;
  border-radius: 25px;
  display:var(--hide);
}

/* ch2 */
#ch2 .ch1-block {
  background:white;
}
#ch2 h1 {
  width:50%;
  position:absolute;
  top:50%;
  transition:1s;
}
#ch2 h1:nth-child(2) {
  right:-50%;
  transition:1s;
}
#ch2 h1:nth-child(2):after {
  content: var(--bBubble);
  position: absolute;
  top: -30%;
  left: -25%;
  display: block;
  font-size: 20px;
  text-align: left;
  opacity:0;
  animation:var(--bAnimation);
}
@keyframes b {
  100% { opacity:1; }
}

/* ch3 */
#ch3 h1:nth-child(1) {
  width:50%;
  position:absolute;
  top:50%;
  transform:scaleX(-1);
  transition:1s;
}
#ch3 h1:nth-child(2) {
  width:50%;
  position:absolute;
  right:-50%;
  top:50%;
  transition:1s;
}
#ch3 h1:nth-child(2):after {
  content: var(--cBubble);
  position: absolute;
  top: -10%;
  left: 0%;
  display: block;
  font-size: 20px;
  text-align: left;
  opacity: 0;
  animation: var(--cAnimation);
}
@keyframes c {
  100% { opacity:1; }
}

#ch3 p, #ch2 p {
  bottom:40%;
  opacity:0;
  transition:.75s;
  font-size:20px;
  font-weight:300;
  text-align:left;
  padding-left:20px;
  width:60%;
}
!

JS 

              
                let root = document.documentElement
var fonts = ['monospace','serif','cursive','sans-serif']
var f = 0
function changeFont(e) {
  f++
  if(f < 3) {
  root.style.setProperty('--fontFamily',fonts[f])  
  } else {
    f = 0
    root.style.setProperty('--fontFamily',fonts[f])  
  }  
  root.style.setProperty('--hide','block')
  root.style.setProperty('--aAnimation','none') 
  document.querySelector('#ch1 .next').style.display = "block"
}

function ch2Open() {
  document.querySelector('.b').style.right = "0"
  root.style.setProperty('--bAnimation','b 1s linear .5s forwards') 
}
function ch2(e) {
  e.style.transform = 'scaleX(-1)'  
  document.querySelector('#ch2 p').style.opacity = "1"
  root.style.setProperty('--bBubble',"''")
  setTimeout(function(){
    document.querySelector('.b').style.right = "-100%"
    document.querySelector('#ch2 .next').style.display = "block"
  },3500)  
}

function ch3Open() {
  document.querySelector('.c').style.right = "0"
  root.style.setProperty('--cAnimation','c 1s linear .5s forwards') 
}
function ch3(e) { 
  document.querySelector('#ch3 p').style.opacity = "1"
  document.querySelector('#ch3 p').innerHTML = '#$%@^!'
  root.style.setProperty('--cBubble',"''")
  setTimeout(function(){
    document.querySelector('.c').style.right = "-100%"
    document.querySelector('#ch3 p').innerHTML = "I guess I am already a big 'A'."
    document.querySelector('#ch3 .next').style.display = "block"
  },1500)    
}

function theEnd() {
  document.querySelector('#title-page').style.paddingTop = '50px'
  document.querySelector('#title-page h1').innerHTML = 'The End'
  document.querySelector('#title-page h3').innerHTML = "no letters were harmed in the making of this production<br><br>don't be like little 'a' y'all"
  document.querySelector('#title-page .next').style.display = 'none'
}
!
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