JSFiddle - React, Tailwind, and code Playground

HTML

<div class="flex-container">
  <div class="flex-inner first">65%</div>
  <div class="flex-inner second">35%</div>
  <div class="flex-inner third">35%</div>
</div>

CSS

.flex-container {
  display: flex;
  flex-direction: column;
  flex-wrap: wrap;
  width: 100vw;
  height: 100vh;
}
.flex-inner {
  display: flex;
  justify-content: center;
  align-items: center;
  color: #fff;
  font-size: 24px;
}
.first {
  background-color: orange;
  width: 65%;
  height: 100%;
}

.second {
  background-color: green;
  width: 35%;
  height: 50%;
}

.third {
  background-color: yellow;
  width: 35%;
  height: 50%;
}