This theme is a bit more complicated than most as it contains multiple files, but it's no more complicated to install! Here are the steps:

1. Download this whole repo as a zip file
2. Extract the contents of the zip file (guides for Windows, Mac and Linux)
3. In Typora, go to:
   1. Preferences
   2. Appearance
   3. Themes
   4. Open theme folder
4. From the extracted zip file, copy the file typora/torillic.css and the folder typora/torillic to the theme folder
5. That's it! It's installed! Just restart Typora and it should appear in your Themes menu.

Happy adventuring!

Well why the heck not! Click here for details about Typora and how to install it.