JSFiddle - React, Tailwind, and code Playground

HTML

<div class="container">
<div class="main-menu">Top</div>
<div class="menu-rest">Top-right</div>
<div class="body">main</div>
</div>

CSS

.container {
    display:flex;
    width: 100%;
    height: 100%;
    flex-wrap: wrap;
  }
  
  .main-menu {
    width: 50%;
    height: 50px;
    background-color: green;
    margin-bottom: 10px;
  }
  
  .menu-rest {
    margin-left: auto;
    margin-top: 20px;
    margin-bottom: 10px;
    width: 40%;
    background-color: lightblue;
  }
  
  .body {
    background-color: purple;
    width: 100%;
    height: 400px;
    display: flex;
  }