JSFiddle - React, Tailwind, and code Playground

HTML

<main id="page" class="page">
  <aside class="page__sidebar">
    <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>
      <li>Menu item 7</li>
    </ul>
  </aside>
  <section class="page__content">
    <button id="button" type="button" @onclick="toggle()">Toggle Sidebar</button>
    <p>Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo consequat. Duis aute irure dolor in reprehenderit in voluptate velit esse cillum dolore eu fugiat nulla pariatur. Excepteur sint occaecat cupidatat non proident, sunt in culpa qui officia deserunt mollit anim id est laborum.</p>
    <p>Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo consequat. Duis aute irure dolor in reprehenderit in voluptate velit esse cillum dolore eu fugiat nulla pariatur. Excepteur sint occaecat cupidatat non proident, sunt in culpa qui officia deserunt mollit anim id est laborum.</p>
  </section>
</main>

CSS

.page {
  position: relative;
  height: 100vh;
  padding-left: 300px;
  transition: padding-left 3s;
}

.page__sidebar {
  box-sizing: border-box;
  padding: 20px;
  width: 300px;
  height: 100%;
  overflow-x: hidden;
  overflow-y: scroll;
  position: fixed;
  top: 0;
  left: 0;
  bottom: 0;
  background: black;
  transition: width 3s;
}

.page__sidebar > ul > li {
  color: #ffffff;
  font-size: 32px;
}

.page__content {
  padding: 20px;
  height: calc(100% - 40px);
  font-size: 32px;
}

.page--min {
  padding-left: 80px;
}

.page--min .page__sidebar {
  width: 80px;
}

JavaScript

let isOpen = true;
const page = document.getElementById('page');
const button = document.getElementById('button');
button.addEventListener('click', () => {
  if (isOpen) page.classList.add('page--min');
  else page.classList.remove('page--min');
  isOpen = !isOpen;
}, false);