How do I get navbar to go 100% of page (not viewport) in css flex-box?

Question

I'm trying to get the navbar to stretch the height of the page.

* {
  box-sizing: border-box;
  padding: 0;
  margin: 0;
}

main {
  display: flex;
  justify-content: flex-start;
  align-items: flex-start;
}

nav {
  display: block;
  width: 60rem;
  background: blue;
  color: white;
  padding: 1rem;
  height: 100%;
}

section {
  padding: 1rem;
}

<main>
  <nav>some nav stuff</nav>
  <section>a tall bodya tall bodya tall bodya tall bodya tall bodya tall bodya tall bodya tall bodya tall bodya tall bodya tall bodya tall bodya tall bodya tall bodya tall bodya tall bodya tall bodya tall bodya tall bodya tall bodya tall bodya tall bodya tall
    bodya tall bodya tall bodya tall bodya tall bodya tall bodya tall bodya tall bodya tall bodya tall bodya tall bodya tall bodya tall bodya tall bodya tall bodya tall bodya tall bodya tall bodya tall bodya tall bodya tall bodya tall bodya tall bodya
    tall bodya tall bodya tall bodya tall bodya tall bodya tall bodya tall bodya tall bodya tall bodya tall bodya tall bodya tall bodya tall bodya tall bodya tall bodya tall bodya tall bodya tall bodya tall bodya tall bodya tall bodya tall bodya tall
    bodya tall bodya tall bodya tall bodya tall bodya tall bodya tall bodya tall bodya tall bodya tall bodya tall bodya tall bodya tall bodya tall bodya tall bodya tall bodya tall bodya tall bodya tall bodya tall bodya tall bodya tall bodya tall bodya
    tall bodya tall bodya tall bodya tall bodya tall bodya tall bodya tall bodya tall bodya tall bodya tall bodya tall bodya tall bodya tall bodya tall bodya tall bodya tall bodya tall bodya tall bodya tall bodya tall bodya tall bodya tall bodya tall
    bodya tall bodya tall bodya tall bodya tall bodya tall bodya tall bodya tall bodya tall bodya tall bodya tall bodya tall bodya tall bodya tall bodya tall bodya tall bodya tall bodya tall bodya tall bodya tall bodya tall bodya tall bodya tall bodya
    tall bodya tall bodya tall bodya tall bodya tall bodya tall bodya tall bodya tall bodya tall bodya tall bodya tall bodya tall bodya tall bodya tall bodya tall bodya tall bodya tall bodya tall bodya tall bodya tall bodya tall bodya tall bodya tall
    bodya tall bodya tall bodya tall bodya tall bodya tall bodya tall bodya tall bodya tall bodya tall bodya tall bodya tall bodya tall bodya tall bodya tall bodya tall bodya tall bodya tall bodya tall bodya tall bodya tall bodya tall bodya tall bodya
    tall bodya tall bodya tall bodya tall bodya tall bodya tall bodya tall bodya tall bodya tall bodya tall bodya tall bodya tall body</section>
</main>