JSFiddle - React, Tailwind, and code Playground

HTML

<header>
  <div class="logo"></div>
</header>
<main>
  <aside class="menu-box"></aside>
</main>

CSS

body, html { margin: 0 }

body, header, main {
  display: flex;
}

header, main {
  justify-content: flex-end;
}

.logo, .menu-box {
  flex-basis: 60px;
}

body {
  flex-direction: column;
  min-height: 100vh;
}

main {
  flex-grow: 1;
  background-color: #ccc;  
}

.logo {
  height: 60px;
  background-color: lightgreen;  
}

.menu-box {
  background-color: green;
}