I wanted to enhance the syntax highlighting in the default Ghost theme (Casper). I dug around and while there are a ton of solutions out there, I settled on Prism because it's simple and lightweight. Notice the colorful goodness:
Prism is easy to install in your default ghost theme (I'm using Casper). Don't let the length of this tutorial fool you; it took me about five minutes total to get up and running.
Go to http://prismjs.com/download.html
Select a few options; basically, which theme you want and what languages you want to support
Scroll down to the bottom and download your custom-made
prism.cssfiles; put them someplace you can find
Copy these files to your server, and login there