JSFiddle - React, Tailwind, and code Playground

HTML

<body>


<main class="outer-wrapper">
    <div class="wrapper">
        <article class="section" id="a"><h2>01</h2></article>
        <article class="section" id="b"><h2>02</h2></article>
        <article class="section" id="c"><h2>03</h2></article>
        <article class="section" id="d"><h2>04</h2></article>
        <article class="section" id="e"><h2>05</h2></article>
        <article class="section" id="f"><h2>06</h2></article>
    </div>
</main>


<!-- MENU _____________________ -->


<header class="large">
    <div class="container">
      <nav>
        <a href="#welcome"><div class="logo"></div></a>
          <ul>
            <li><a href="#a">01</a></li>
            <li><a href="#b">02</a></li>
            <li><a href="#c">03</a></li>
            <li><a href="#d">04</a></li>
         </ul>
      </nav>
    </div>
  </header>
  
  
</body>

CSS

body {
  margin: 0;
  padding: 0;
}

.outer-wrapper {
  width: auto;
  height: 100vw;
  transform: rotate(-90deg) translateX(-100vh);
  transform-origin: top left;
  overflow-y: scroll;
  overflow-x: hidden;
  position: absolute;
  scrollbar-width: none;
  -ms-overflow-style: none;
  scroll-behavior: smooth;
}

::-webkit-scrollbar {
  display: none;
}

.wrapper {
  display: flex;
  flex-direction: row;
  width: auto;
  transform: rotate(90deg) translateY(-100vh);
  transform-origin: top left;
    margin: 0;
  padding: 0;
}

.section {
	color: #000;
  width: 100vw;
  height: 100vh;
}

#a { background-color: #ccc; }
#b { background-color: #fff; }
#c { background-color: #ccc; }
#d { background-color: #fff; }
#e { background-color: #ccc; }
#f { background-color: #fff; }


h2 {
text-align: center;
font-size: 200px;
margin: 0;
}



/* MENU  _________________________ */



.logo {
  float: left;
}

nav {
  width: 100%;
}

/* HEADER */

header {
  float: left;
  width: 100%;
  position: absolute;
  z-index: 9999;
}


/* HEADER LARGE */

header.large {
  height: 50px;
}

header.large .logo {
  width: 225px;
  height: 50px;
  margin: 20px 0 0 20px;
  background: url('../images/logo-fireqa-green-500px.png');
  background-repeat: no-repeat;
  background-size: contain;

  transition: 0.7s all;
  -moz-transition: 0.7s all;
  -webkit-transition: 0.7s all;
  -o-transition: 0.7s all;
}


/* UNORDERED LIST */

header.large ul {
  list-style: none;
  float: right;
  margin-right: 25px;
}
header.small ul {
  list-style: none;
  float: right;
  margin: 0;
}

header.large li {
  display: inline;
  float: left;
  list-style-position: inside;
  height: 50px;
  -webkit-transition: all ease 0.3s;
  -moz-transition: all ease 0.3s;
  transition: all 0.3s ease-in-out;
}


header.large li a {
  display: block;
  padding: 20px;
  color: #0E6245;
  text-decoration: none;
  font-family: 'Montserrat', 'arial', sans-serif;
  font-weight: 600 !important;
  letter-spacing: -1px;
  font-size: 25px;

...