JSFiddle - React, Tailwind, and code Playground

HTML

<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="utf-8" />
    <title>Layout</title>
  </head>
  <body>
    <div class="wrapper">
      <header></header>
      <main>
        <div class="sidebarleft"></div>
        <div class="data">
          <div class="textcontent">
            <textarea class="input-textarea"></textarea>
            <button class="button1">button1</button>
            <div class="result-text">
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CSS

html,
body {
  margin: 0;
  background-color: gray;
}

.wrapper {
  height: 100vh;
  display: flex;
  flex-direction: column;
}

main {
  display: flex;
  flex: 1;
  background-color: #00ac17;
}

header {
  height: 35px;
  background-color: #004d20;
}

footer {
  height: 25px;
  background-color: #49fa7e;
  color: rgb(19, 19, 19);
}

.sidebarleft {
  flex: 0 0 55px;
  background-color: blue;
}


.data {
  flex-grow: 1;
  background-color: rgb(185, 46, 46);
}

.textcontent {
  display: flex;
  flex-direction: column;
  height: 100%;
  width: 50%;
  float: left;
  background-color: rgb(152, 43, 255);
}

.diagram {
  height: 100%;
  width: 50%;
  float: left;
  background-color: rgb(113, 1, 165);
}

.input-textarea {
  resize: none;
  height: 100px;
}

.result-text {
  background-color: grey;
  flex: 1;
  overflow: scroll;
  text-align: justify;
  padding: 20px;
}

.button1 {
  flex: 0;
}

.button2 {
  flex: 1;
}

.button3 {
  flex: 1;
}