Боковое выезжающее меню

<div class="btn btnOpen">
  <svg xmlns="http://www.w3.org/2000/svg" width="24" height="24" viewBox="0 0 24 24">
    <path d="M0 0h24v24H0z" fill="none" />
    <path d="M20 11H7.83l5.59-5.59L12 4l-8 8 8 8 1.41-1.41L7.83 13H20v-2z" />
  </svg>
</div>

<div class="btn btnClose">
  <svg xmlns="http://www.w3.org/2000/svg" width="24" height="24" viewBox="0 0 24 24">
    <path d="M19 6.41L17.59 5 12 10.59 6.41 5 5 6.41 10.59 12 5 17.59 6.41 19 12 13.41 17.59 19 19 17.59 13.41 12z" />
    <path d="M0 0h24v24H0z" fill="none" />
  </svg>
</div>

<ul>
  <li>Menu Item 1</li>
  <li>Menu Item 2</li>
  <li>Menu Item 3</li>
  <li>Menu Item 4</li>
  <li>Menu Item 5</li>
  <li>Menu Item 6</li>
</ul>

<h1>Click the arrow</h1>

*, :before, :after {
  box-sizing: border-box;
}

html, body {
  width: 100%;
  height: 100%;
  margin: 0;
}

html {
  font-size: 10px;
  font-family: "Courier New", Courier, monospace;
}

body {
  display: flex;
  align-items: center;
  justify-content: center;
  background-image: linear-gradient(135deg, #5EFCE8 0%, #736EFE 100%);
  overflow: hidden;
}

.btn {
  position: absolute;
  top: 2rem;
  right: 2rem;
  z-index: 10;
  width: 60px;
  height: 60px;
  display: flex;
  align-items: center;
  justify-content: center;
  border-radius: 0;
  -webkit-user-select: none;
     -moz-user-select: none;
      -ms-user-select: none;
          user-select: none;
  cursor: pointer;
  transition: background 0.1s ease-in-out;
}

.btnOpen:hover {
  background-color: #fff;
}

.btnClose {
  z-index: 9;
  -webkit-transform: translateX(70px);
          transform: translateX(70px);
  opacity: 0;
}
.btnClose:hover {
  background-color: #5EFCE8;
}

ul {
  position: fixed;
  top: 0;
  right: 0;
  width: 300px;
  height: 100%;
  margin: 0;
  padding: 10rem 0 0;
  list-style: none;
  background-color: white;
  -webkit-transform: translateX(300px);
          transform: translateX(300px);
}

li {
  position: relative;
  font-size: 2rem;
  padding: 2rem 0 2rem 4rem;
  -webkit-user-select: none;
     -moz-user-select: none;
      -ms-user-select: none;
          user-select: none;
  cursor: pointer;
  transition: background 0.2s ease-in;
}
li:hover {
  background-color: #5EFCE8;
}

const btnOpen = document.querySelector('.btnOpen');
const btnClose = document.querySelector('.btnClose');


// ---------------


const tl = new TimelineMax({paused: true});

tl.timeScale(1);

tl.to('h1', 0.3, { opacity: 0 })

  .to(btnOpen, 0.5, {
    x: -300,
    opacity: 0,
    ease: Power2.easeInOut,
  }, '-=0.5')

  .to('ul', 0.5, {
    x: 0,
    ease: Power2.easeInOut,
  }, '-=0.5')

  .to(btnClose, 0.5, {
    x: 0,
    opacity: 1,
    rotation: 360,
    ease: Power1.easeInOut,
  }, '-=0.5')


  .staggerFrom('li', 0.2, {
    opacity: 0,
    x: 70,
    ease: Back.easeOut,
  }, 0.06, '-=0.18');


// ---------------


openMenu = () => tl.play();
closeMenu = () => tl.reverse();

btnOpen.addEventListener('click', openMenu, false);
btnClose.addEventListener('click', closeMenu, false);