<div class="example">
  <header>
    header content here
  </header>
  <main class="main">
    <nav>
      nav content here
    </nav>
    <div class="content">
      main content here
    </div>
    <aside>
      aside content here
    </aside>
  </main>
  <footer>
    footer content here
  </footer>
</div>

* {
  box-sizing: border-box;
}

*:before, *:after {
  box-sizing: inherit;
}

body {
  width: 100%;
  height: 100%;
  overflow-x: hidden;
  font-size: 100%;
  line-height: 1.5;
}

.example {
  width: 100%;
  max-width: 1200px;
  height: 700px;
  margin: 0 auto;
}

header, footer {
  width: 100%;
  padding: 1em;
  text-align: center;
  font-size: 2rem;
  background-color: coral;
}

.main {
  display: flex;
  height: 100%;
  font-size: 2rem;
}

nav, aside {
  padding: 1em;
}

nav {
  background-color: lightblue;
}

aside {
  background-color: lightgreen;
}

.content {
  background-color: orange;
  padding: 1em;
  order: -1;
}

footer {
  align-self: flex-end;
}