<button class="open">Open</button>
<div class="menu">
  <nav class="nav">
    <ul class="nav__list">
      <li class="nav__item"><a href="" class="nav__link">Link</a></li>
      <li class="nav__item"><a href="" class="nav__link">Link</a></li>
      <li class="nav__item"><a href="" class="nav__link">Link</a></li>
      <li class="nav__item"><a href="" class="nav__link">Link</a></li>
      <li class="nav__item"><a href="" class="nav__link">Link</a></li>
    </ul>
    <button class="clouse">Clouse</button>
  </nav>
</div>

* {
  box-sizing: border-box;
}
body {
  min-height: 100vh;
  position: relative;
  overflow: hidden;
}
.menu {
  width: 300px;
  height: 100%;
  padding: 20px;
  background: #000;
  position: absolute;
  top: 0;
  right: -300px;
  transition: transform .5s;
  &--open {
    transform: translateX(-300px);
  }
}
.nav {
  position: relative;
  button {
    position: absolute;
    top: 0;
    right: 0;
  }
  &__list {
    list-style-type: none;
    margin: 0;
    padding: 0;
  }
  &__item {
    padding: 3px 0;
  }
  &__link {
    text-decoration: none;
    color: #fff;
    font-size: 18px;
  }
}

const menu = document.querySelector('.menu');
const open = document.querySelector('.open');
const clouse = document.querySelector('.clouse');

open.addEventListener('click', () => {
  menu.classList.add('menu--open')
})

clouse.addEventListener('click', () => {
  menu.classList.remove('menu--open')
})