Add different theming options

```
Love the editor! Nice work!

One enhancement request would be to add different theming options.  I use your 
plugin with a dark theme so all the color clash.  A few different options for 
both light and dark would be awesome!

Thanks for the hard work!

```

Original issue reported on code.google.com by `troy.gro...@gmail.com` on 19 Dec 2014 at 4:15
