JSFiddle - React, Tailwind, and code Playground

HTML

<!DOCTYPE html>
<html lang="en">

  <head>
    <meta charset="utf-8">
    <title>JavaScript Basics</title>
    <meta name="viewport" content="width=device-width, initial-scale=1">
    <link href="https://fonts.googleapis.com/css?family=Lato|Raleway" rel="stylesheet">
    <link rel="stylesheet" href="styles.css">
  </head>

  <body>

    <div class="container">

      <nav id="navbar">
        <header>
          <h1>JavaScript Basics</h1>
        </header>

        <a class="nav-link" href="#JavaScript_and_Java" rel="internal">
          <div class="nav-link-container">JavaScript and Java</div>
        </a>
        <a class="nav-link" href="#Hello_world" rel="internal">
          <div class="nav-link-container">Hello world</div>
        </a>
        <a class="nav-link" href="#Variables" rel="internal">
          <div class="nav-link-container">Variables</div>
        </a>
        <a class="nav-link" href="#Declaring_variables" rel="internal">
          <div class="nav-link-container">Declaring variables</div>
        </a>
        <a class="nav-link" href="#Variable_scope" rel="internal">
          <div class="nav-link-container">Variable scope</div>
        </a>
        <a class="nav-link" href="#Global_variables" rel="internal">
          <div class="nav-link-container">Global variables</div>
        </a>
        <a class="nav-link" href="#Constants" rel="internal">
          <div class="nav-link-container">Constants</div>
        </a>
        <a class="nav-link" href="#Data_types" rel="internal">
          <div class="nav-link-container">Data types</div>
        </a>
        <a class="nav-link" href="#if...else_statement" rel="internal">
          <div class="nav-link-container">if...else statement</div>
        </a>
        <a class="nav-link" href="#while_statement" rel="internal">
          <div class="nav-link-container">while statement</div>
        </a>
        <a class="nav-link" href="#Function_declarations" rel="internal">
          <div...

CSS

html {
  /* Applying so that 1rem will equal 10px for easier calculation; default font-size in browsers is 16px, and 62.5% of 16px is 10px. 0.1rem now equals 1px, 1.6rem = 16px */
  font-size: 62.5%;
  scroll-behavior: smooth;
}

#main-doc {padding-top: 0}

body {
  font-size: 1.6rem;
  font-family: Raleway, sans-serif;
  margin: 0;
}

.container {
  display: grid;
  grid-template-columns: 20% 1fr;
  grid-template-rows: 1fr;
  grid-template-areas: "nav main" "nav main"
}

/* Tells browser to account for any border and padding in the values specified for an element's width and height */

* {
  box-sizing: border-box;
}

nav {
  grid-area: nav;
  /* Alternative to position: fixed that is compatible with CSS grid to keep navbar in place. Doesn't remove anything from document flow */
  position: sticky;
  /* Keeps it at top of screen at all times */
  top: 0;
  height: 100vh;
  background: linear-gradient(#f4f4f4, #cbcbcb);
}

h1 {
  font-size: 1.5em;
  font-family: Lato, sans-serif;
  padding-left: 3.75rem;
}

h2:first-of-type {
  margin-top: 0;
}

.nav-link {
  width: 100%;
  color: black;
}

.nav-link-container {
  padding: 0.5rem 0 0.5rem 3.75rem;
  margin: 0.5rem 0;
}

.nav-link-container:hover {
  background: linear-gradient(to right, rgba(147, 206, 222, 1) 0%, rgba(117, 189, 209, 1) 41%, rgba(95, 176, 199, 1) 100%);
}

a {
  text-decoration: none;
}

main {
  grid-area: main;
  padding: 3rem;
}

main a {
  color: #5eb0c7;
  font-weight: 400;
}

code {
  display: block;
  text-align: left;
  white-space: pre;
  position: relative;
  word-break: normal;
  word-wrap: normal;
  line-height: 2;
  background: linear-gradient(to right, rgba(147, 206, 222, 1) 0%, rgba(117, 189, 209, 1) 41%, rgba(95, 176, 199, 1) 100%);
  color: #fff;
  border-radius: 5px;
  font-size: 14px;
  padding: 15px;
  margin: 10px;
  transition-property: transform, box-shadow;
  transition-duration: .25s;
  transition-timing-function: linear;
}

code:hover {
  transform: scale(1.01);
 ...