Ruby on Rails Calling Object Stylesheet Error

First-time post. I'm having trouble referencing a stylesheet with Ruby on Rails for my Web Dev 1 class. I've found similar posts both here:

https://www.pixelstech.net/article/1476434897-Resolve-stylesheet_link_tag-fails-to-work-in-Ruby-on-Rails

and

TypeError: Object doesn't support this property or method

but my code doesn't seem to change, regardless of whether I change anything in application.html.erb or adding coffee-source to the gem. I still get an error message, and when I tried the workaround it's as if the code hasn't changed at all:

https://imgur.com/a/iqHf7

I'm sure this is quite a basic issue, but I'm quite lost. Any ideas?

Thanks and have a great day!