JSFiddle - React, Tailwind, and code Playground

HTML

<link rel="stylesheet" href="https://cdnjs.cloudflare.com/ajax/libs/font-awesome/5.15.4/css/all.min.css">
 <div class="app">
      <div class="content">
        content
        <button id="collapseBtn" onclick="toggleCollapseMenu()">
          collapse
        </button>
      </div>
      <div id="mainMenu" class="menu">
        <div class="menu-container">
          <ul>
            <li>
              <a>
                <div class="nav-link-container">
                  <span class="nav-link-icon"><i class="fas fa-home"></i></span>
                  <span class="nav-link-text">One two</span>
                </div>
              </a>
            </li>

            <li>
              <a>
                <div class="nav-link-container">
                  <span class="nav-link-icon"><i class="fas fa-home"></i></span>
                  <span class="nav-link-text">One two three</span>
                </div>
              </a>
            </li>
            <li>
              <a>
                <div class="nav-link-container">
                  <span class="nav-link-icon"><i class="fas fa-home"></i></span>
                  <span class="nav-link-text">One two three four</span>
                </div>
              </a>
            </li>
            <li>
              <a>
                <div class="nav-link-container">
                  <span class="nav-link-text">no icon</span>
                </div>
              </a>
            </li>
            <li>
              <a>
                <div class="nav-link-container">
                  <span class="nav-link-text">no icon</span>
                </div>
              </a>
            </li>
            <li>
              <a>
                <div class="nav-link-container">
                  <span class="nav-link-text">no icon</span>
                </div>
              </a>
            </li>
            <li>
              <a>
                <div class="nav-link-container">
                  <span...

CSS

:root {
  --height: 150px;
}

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

ul {
  list-style-type: none;
  padding: 0;
  margin: 0;
}

a {
  text-decoration: none;
}

.app {
  height: 100%;
  display: flex;
  flex-direction: column;
  overflow: hidden;
}

#collapseBtn {
  display: inline-block;
  cursor: pointer;
  background-color: black;
  color: white;
  padding: 0.5rem;
  box-sizing: border-box;
  position: fixed;
  top: 0;
  z-index: 999;
  border: unset;
  
  width: 200px;
  height: 100px;
}

#collapseBtn:hover {
  background-color: gray;
}


.menu,
.content {
  width: 100%;
}

.menu {
  background-color: black;
  transition: height 0.8s ease-in;
  height: var(--height);
  overflow: hidden;
}

.content {
  background-color: burlywood;
  flex: 1;

  overflow: auto;
  margin: auto;
}

.menu-container {
  overflow-y: hidden;
  overflow-x: auto;

  height: 100%;
  width: 100%;

  height: var(--height);
  position: absolute;
  bottom: 0;

  -webkit-transition: height 0.2s ease-in;
  -moz-transition: height 0.2s ease-in;
  -o-transition: height 0.2s ease-in;
  transition: height 0.2s ease-in;
}

.menu-container ul {
  background-color: #587c34;
  display: flex;
  flex-direction: column;
  flex-wrap: wrap;
  height: 100%;
  padding: 1rem;
  box-sizing: border-box;
  
  min-width: 100%;
  width: 100%;
  margin: auto;
}

.menu-container ul li {
  min-width: var(--height);
  border: 1px solid white;

  box-sizing: border-box;

  height: 100%;
  max-height: var(--height);
}

.menu-container ul li a {
  display: block;
  width: 100%;
  height: 100%;
  padding: 0.2rem;
  box-sizing: border-box;
}

.menu-container .nav-link-container {
  display: flex;
  flex-direction: column;
  background-color: #f55858;
  justify-content: center;
  text-align: center;
  align-items: center;

  height: 100%;

  justify-content: start;
}

.menu-container span.nav-link-icon {
  background-color: magenta;
  font-size:...

JavaScript

function toggleCollapseMenu() {
      document.getElementById("mainMenu").classList.toggle("uncollapsed");
    }