JSFiddle - React, Tailwind, and code Playground

HTML

<div class="a">
  <div class="b1">
    <p>hurr durr</p>
    <p>hurr durr</p>
    <p>hurr durr</p>
    <p>hurr durr</p>
    <p>hurr durr</p>
    <p>hurr durr</p>

  </div>
  <div class="b2">
    <div class="c">
      miksi et ole full height saatana
    </div>
  </div>
</div>

CSS

.a {
  background-color: red;
  display: flex;
  height: 100%;
}

.b1 {
  flex-grow: 0;
  background-color: green;
}

.b2 {
  flex-grow: 2;
  background-color: yellow;
}

.c {
  height: 100%;
  background-color: blue;
}