broken theme – style sheet missing

Hello,

New to WordPress and have little knowledge of coding.

I purchased this theme https://www.templatemonster.com/demo/32327.html
and installed to my host for our site https://portsmouthmfa.org/wordpress/

I uploaded the zipped source file to my host file manager and unarchived. I also uploaded a theme folder that contains an index.php and style.ccs.

What loaded is a barebones layout of the theme. I thought it would load with the layout and functionality seen in the preview. Was that a wrong assumption? Is there a way to activate the completed design as it was advertised?

Is this related to the Broken Theme message?
Name: sources
Description: stylesheet is missing

Thank you!