Themes - ghostselfbot/ghost GitHub Wiki
Ghost features a multi-file shareable theming system. This page will show you how to create and install themes.
Creating a theme
To create a theme in Ghost. Go to the settings page (gear icon) in the GUI and expand the theming section. This is where you can create, select and delete themes. If you want to install a theme file, click on the folder button next to the delete button, this will open the themes folder. Put your theme file here and the theme should appear in the select theme drop down. If it doesn't restart Ghost.