JSFiddle - React, Tailwind, and code Playground

HTML

<div class="container">
  <div class="child half">
    HALF
  </div>
  
  <div class="child half">
    HALF
  </div>
  
   <div class="child">
    FULL
  </div>
   <div class="child">
    FULL
  </div>
  <div class="child">
    FULL
  </div>
   <div class="child">
    FULL
  </div>
</div>

CSS

div {
  border: 1px solid;
}

.container {
  width: 400px;
  display: flex;
  flex-direction: column;
}
.child {
  
  height: 200px;
}
.child.half {
  flex: 1 1 10em;
  color: green;
}

.child:not(.half) {

  flex-shrink: 2;
  flex-basis: 50%;
  color: purple; 
}