How do I make my vertical side menu take up the entire screen

Question

The navigation bar in my webpage (below) only takes up a small part of the vertical, but I want it to take up the entire vertical. In the CSS file (below) in the.sidenav class I set the height property to 100%, which I thought would solve the problem, but it didn't.

This is my html body (ignore what's between the {% %} that is Django syntax)

{% extends "myapp/layout.html" %}

{% block body %}
<ul class="sidenav">
  <li><a id="active" href="default.asp">Home</a></li>
  <li><a href="news.asp">News</a></li>
  <li><a href="contact.asp">Contact</a></li>
  <li><a href="about.asp">About</a></li>
</ul>
{% endblock %}

Here is my CSS

body {
  margin: 0;
  font-family: Arial, Helvetica, sans-serif;
}

ul {
  list-style-type: none;
  margin: 0;
  padding: 0;
}

.sidenav {
  overflow: hidden;
  background-color: #b3b3b3;
  width: 10%;
  height: 100%;
}

.sidenav a {
  color: #f2f2f2;
  text-align: center;
  padding: 20px 30px;
  text-decoration: none;
  font-size: 17px;
  display: block;
}

.sidenav a:hover {
  background-color: #e6e6e6;
  color: black;
}

.sidenav a#active {
  background-color: #4d4d4d;
  color: white;
}

And here is my webpage so far

Answer 1

Try using vh(viewport height) as height unit:

.sidenav{
min-height: 100vh
}

Answer 2

The solution is to say

height: 100vh;

If you set height to 100%, it will orientate on the parent(root) therefore you would have to set

html{height: 100%}

Answer 3

You can also do the following:

html {
  height: 100%;
  width: 100%;
}
body {
  margin: 0;
  font-family: Arial, Helvetica, sans-serif;
  height: 100%;
  width: 100%;
}

I share a codesandbox with your complete code