How to use CSS to color the background of a website a color?

Link To Code: https://codepen.io/triplefire99/pen/xLgxgQ

I tried doing the following code, and it didn’t work, any thoughts on doing this?

The “correct” way to do this:

<style>
  .mybackground{
    background-color: #006666;
  }
</style>
<body class="mybackground">
</body>

But note that on CodePen the HTML tab is meant for everything inside the <body> and the CSS tab for everything inside <style>.

I see, didn’t background-color correctly. Thanks for the help!