* Added examples and definition - CSS
- added two examples with the most used values
- added definition
* Added resources to Graceful Degradation - CSS
Added links to multiple articles / post / explanations / tools to help coders understand the concept
* changed triple backtick to single
* fixed https link
- had to fix one link to point to the https site
- removed one link because it doesn't match with the guide provided by FCC
* Add a space between class name and curly brace