What is BEM naming convention?
Image result for bem naming convention
BEM stands for block, element, and modifier. 
It's a naming convention that divides the user interface into small, 
reusable components that will prepare us for the changes in design of 
our websites. This convention also enhances the cross-site copy/paste feature 
by helping make elements reusable components.

.block__elem { }

.block__elem--mod { }

.block__elem--mod { }