Preserve white-space in Page

You are not wrapping the code inside <code> tags.

<pre>
<code>    
selector {
           property: value;
           property: value;
        }
</code>
</pre>

Furthermore, most syntax highlighting plugins also use this format (both <pre> and <code>) to render code.
Here you have more about this.
https://css-tricks.com/snippets/css/make-pre-text-wrap/