There are a lot of great resources to help you create better CSS code.
I will add on to this article when I find additional resources that I find useful.
Force CSS and JS changes to go live immediately
(Very useful when the browser is not showing your updates right away as your working on the site.)
Image effects and image hover effects
Hover over buttons and create an icon effect:
Picks up colors from web sites with stylifyme.
designyourway – material design resources for designers
Long lists of great resources to go through:
designyourway – the most popular css libraries that are on github
Simplilearn – css3 resources ultimate list article
22 Essential CSS Recipes