I had a look. Your site’s CSS is located at https://www.ubongogamelab.com/styles/main.css
And yet in the source the URL points to https://ubongogamelab.com/styles/main.css
In your site’s config.toml please set the baseURL parameter to the www version of your website so that the stylesheet loads properly.
EDIT
Also changed the title of the topic because this issue does not seem related to the Osprey Theme but rather it has to do with your project’s baseURL configuration.