JSFiddle - React, Tailwind, and code Playground

HTML

<div class="container">
  <div class="left">
    ASIDE
    ASIDE
    ASIDE
    ASIDE
    ASIDE
  </div>
  <div class="rightTop">RIGHT TOP</div>
  <div class="rightBottom">RIGHT BOTTOM</div>
</div>

CSS

.container {
  display: flex;
  flex-wrap: wrap;
}

.left {
  flex: 15%;
  background-color: rgb(255, 0, 0);
}

.rightTop {
  flex: 85%;
  background-color: rgb(0, 255, 0);
  align-self: flex-start;
}

.rightBottom {
  flex: 85%;
  background-color: rgb(0, 0, 255);
}