This is for my own reference as much as anything else.

  1. Go here https://cdnjs.com/libraries/prism
  2. Copy the CSS and JS for the features and theme you want
  3. Add them as <link> or <script> as appropriate to your code injection section in the Ghost Blog Admin  (I put them in the footer)
  4. Add the language to your Markdown code blocks
<script src="https://cdnjs.cloudflare.com/ajax/libs/prism/1.16.0/prism.min.js"></script>
<link rel="stylesheet" type="text/css" href="https://cdnjs.cloudflare.com/ajax/libs/prism/1.16.0/plugins/line-numbers/prism-line-numbers.min.css" />
<link rel="stylesheet" type="text/css" href="https://cdnjs.cloudflare.com/ajax/libs/prism/1.16.0/themes/prism-okaidia.css" />

<script src="https://cdnjs.cloudflare.com/ajax/libs/prism/1.16.0/components/prism-csharp.min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/prism/1.16.0/components/prism-css.min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/prism/1.16.0/components/prism-clike.min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/prism/1.16.0/components/prism-javascript.min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/prism/1.16.0/components/prism-markdown.min.js"></script>

Markdown Sample

```csharp
public static void sayHello(){
 Console.WriteLine("Hello, world");
}
```

Displays as

 public static void sayHello(){
     Console.WriteLine("Hello, world");
 }