<div class="app">
  <header>
    Basic Application
  </header>
  <main>
    <!-- Left sidebar -->
    <aside></aside>

    <!-- Main content -->
    <article>
      <p>
       Why do Java developers wear glasses? ... Because they don't C#.
      </p>

    </article>

  </main>
</div>

:root {
/*   Background Colors */
  --headerBg: #001b38;
  --sidebarBg: #ba324f;
  --articleBg: #f2f2f4;
/*   Text Colors */
  --articleTextColor: #999999;
  --headerTextColor: #ffffff;
}

.app {
  display: flex;
  flex-direction: column;
  height: 100vh;
}
header {
  background: var(--headerBg);
  padding: 10px;
  color: var(--headerTextColor);
}
main {
  flex-grow: 1;
  display: flex;
  flex-direction: row;
}
aside {
  min-width: 150px;
  background: var(--sidebarBg);
}
article {
  flex-grow: 1;
  background: var(--articleBg);
  padding: 10px 20px;
  font-size: 28px;
  color: var(--articleTextColor);
  
}