I think this post is largely bad advice. Passing a block of CSS to a developer doesn’t translate the needs of the design in any way more clearly than a written/spoken sentence, unless the designer and developer are not speaking the same language (meaning one speaks French and the other Mandarin).
I worked at a company where the Design Team knew just enough about CSS to dev-inspect finished work and complain about font-sizes not being the right pixel size (they were in em measurements for responsive design) or margins not being exact (in responsive layouts where the margins changed as a percentage), etc.
Communication does go both ways, but being handed a `corrected` block of CSS in those cases was more of an insult to the craft of Front End Development by Designers who thought they knew better about code than the Developers. At that point it’s not time for the Designers to learn to code, it’s time to understand the difference between creating a mockup with Photoshop/Illustrator/Sketch (with non-web-standard type foundries) and Developing a functional user interface with all the media queries in place.
If a designer is having trouble getting a developer to SEE a border or a color or a shadow within a mockup, I don’t think the problem will be solved by having the designer write CSS corrections — there’s something else missing in the communication between them.