You can learn more about writing code in your post at the link here: http://codex.wordpress.org/Writing_Code_in_Your_Posts

Default Style

<!DOCTYPE html>
<html>
<head>
  <meta charset="utf-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <title>Site Title</title>
</head>

Markup

<pre>
code goes here...
</pre>

Light Style

<!DOCTYPE html>
<html>
<head>
  <meta charset="utf-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <title>Site Title</title>
</head>

Markup

<pre class="prettyprint prettyprint-light linenums">
code goes here...
</pre>

Dark Style

<!DOCTYPE html>
<html>
<head>
  <meta charset="utf-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <title>Site Title</title>
</head>

Markup

<pre class="prettyprint linenums">
code goes here...
</pre>