<div id='rocket'></div>
<div id='exhaust'></div>
<div id='sky'></div>
<section>scroll to launch</section>
<section></section>
<section></section>
<section></section>

:root {
  --base-padding: 3vw;
  --white-25: rgba(255,255,255,.25);
  --white-50: rgba(255,255,255,.5);
}
body {
  margin: var(--base-padding);
  font-family: system-ui;
}

* {
  box-sizing: border-box;
}

section {
  display: block;
  min-height: 100vh;
  display: grid;
  place-items: center;
}

#rocket {
  width: 40px;
  height: 125px;
  background:
    linear-gradient(to right, transparent 45%, firebrick 45%, firebrick 55%, transparent 55%),
    radial-gradient(circle at 50% 40%, rgba(255,255,255,1) 10%, #aaa 11%, #aaa 15%, transparent 16%),
    linear-gradient(to right, transparent 50%, rgba(0,0,0,.1) 50%),    
    linear-gradient(to bottom, firebrick 12%, transparent 12%),
    lightgray;
  background-size: 100% 40%, 100% 100%, 100% 100%, 100% 100%, 100% 100%, 100% 100%;
  background-position: 50% 95%, 0 0, 0 0, 0 0, 0 0;
  background-repeat: no-repeat;
  border-radius: 50px 50px 50px 50px / 200px 200px 10px 10px;  
  position: fixed;
  bottom: 0;
  left: calc(50% - 20px);
  box-shadow: 0 15px 0 -5px #666;
  filter: drop-shadow(0px -5px 2px rgba(0,0,0,.15));
}

#rocket:before {
  content:'';
  width: 200%;
  height: 50%;
  position: absolute;
  top: 55%;
  left: -50%;
  background: 
    radial-gradient(circle at 50% 100%, transparent 50%, firebrick 51%);
  clip-path: polygon(0% 0%, 25% 0%, 25% 100%, 75% 100%, 75% 0%, 100% 0%, 100% 100%, 0% 100%);
  border-radius: 100% 100% 0 0;
}
#rocket:after {
  content:'';
  width: 60%;
  height: 25%;
  position: absolute;
  top: 108%;
  left: 20%;
  background:
    linear-gradient(to bottom, orangered, gold);
  border-radius: 0 0 25% 25%;
  filter: blur(2px);
  opacity: .5;
  animation: blast_off .25s linear infinite;
}

@keyframes blast_off {
  33% { 
    background:
      linear-gradient(to bottom, orangered 25%, gold 75%);
  }
  66% { 
    background:
      linear-gradient(to bottom, orangered 50%, gold 90%);
  }
}


.shake_rocket {
  animation: shake .1s linear infinite;
}
@keyframes shake {
  25% { transform: translateX(-1px); }
  75% { transform: translateX(1px); }
}

#sky {
  min-height: 200vh;
  width: 100%;
  position: fixed;
  bottom: 0;
  left: 0;
  background: 
    radial-gradient(circle at 75% 24%, rgba(255,255,255,.5) .25%, transparent .25%),
    radial-gradient(circle at 10% 23%, rgba(255,255,255,.25) .25%, transparent .25%),
    radial-gradient(circle at 98% 29%, rgba(255,255,255,.25) .25%, transparent .25%),
    radial-gradient(circle at 63% 10%, rgba(255,255,255,.25) .25%, transparent .25%),
    radial-gradient(circle at 20% 6%, rgba(255,255,255,.25) .25%, transparent .25%),
    radial-gradient(circle at 75% 5%, rgba(255,255,255,.25) .25%, transparent .25%),
    radial-gradient(circle at 35% 15%, rgba(255,255,255,.25) .25%, transparent .25%),
    radial-gradient(circle at 94% 10%, rgba(255,255,255,.25) .25%, transparent .25%),
    radial-gradient(circle at 55% 30%, rgba(255,255,255,.25) .25%, transparent .25%),
    radial-gradient(circle at 4% 40%, rgba(255,255,255,.25) .25%, transparent .25%),
    radial-gradient(circle at 91% 35%, rgba(255,255,255,.25) .25%, transparent .25%),
    radial-gradient(circle at -1% 3%, rgba(0,0,0,.15) 2%, transparent 2.5%),
    radial-gradient(circle at 11% 6.5%, rgba(0,0,0,.15) 1%, transparent 1.5%),
    radial-gradient(circle at 15% 0%, rgba(0,0,0,.15) 2%, transparent 2.5%),
    radial-gradient(circle at 5% 8%, rgba(0,0,0,.15) 2%, transparent 2.5%),
    radial-gradient(circle at -5% -5%, rgba(255,255,255,.15) 9%, transparent 10%),
    radial-gradient(circle at 0% 0%, #888 10%, transparent 12%),
    linear-gradient(to top, beige, #306);
  z-index: -1;
}

#exhaust {
  width: 400px;
  height: 100px;
  position: fixed;
  bottom: -50px;
  left: calc(50% - 200px);
  opacity: 0;
  transition-origin: 50% 100%;
  transition: 1s;
}
#exhaust:after {
  content: '';
  width: 400px;
  height: 100px;
  position: absolute;
  bottom: 0;
  left: 0;
  background:
    radial-gradient(circle at 20% 90%, white 50px, transparent 51px),
    radial-gradient(circle at 35% 115%, white 50px, transparent 51px),
    radial-gradient(circle at 50% 135%, white 50px, transparent 51px),
    radial-gradient(circle at 65% 115%, white 50px, transparent 51px),
    radial-gradient(circle at 80% 90%, white 50px, transparent 51px);
  filter: blur(1px) drop-shadow(0px -5px rgba(0,0,0,.025));
  animation: shake .1s linear infinite;
}

.exhaust {
  opacity: 1 !important;
  bottom: 0 !important;
}

const rocket = document.querySelector('#rocket')
const sky = document.querySelector('#sky')
const ex = document.querySelector('#exhaust')
var bottom = 0
var last_y = 0
var wheel;

window.addEventListener('wheel', function(e){
  wheel = e.deltaY
})

window.addEventListener('scroll', function(e){
  var h = window.innerHeight
  var y = document.documentElement.scrollTop
  var doc = document.body.offsetHeight - 250
  var perc = y / (doc - h)
  // console.log(perc)

  if(perc < 1){
    sky.style.bottom = -1*(perc)*100 + '%'    
  }  

  if(perc > 0) {
    rocket.classList.add('shake_rocket')
    ex.classList.add('exhaust')
  } else {
    rocket.classList.remove('shake_rocket')
    ex.classList.remove('exhaust')
  }
  
  if(perc > .37) {
    ex.classList.remove('exhaust')
  }

  if(perc > .25) {
    bottom = (perc - .25)*133
  }
  
  if(perc > 0) {
    bottom = (perc - .25)*133
    if(perc - .25 < 0) {
      bottom = 0
    }
  }
  rocket.style.bottom = bottom + '%'

  last_y = y
})