These guidelines are influenced and inspired by http://sass-guidelin.es/ and http://cssguidelin.es/.They provide rules for writing consistent, maintainable code across multiple developers and deployers.

Harry Roberts sums it up well in CSS Guidelines:

A coding styleguide (note, not a visual styleguide) is a valuable tool for teams who:

• build and maintain products for a reasonable length of time
• have developers of differing abilities and specialties
• have a number of different developers working on a product at any given time
• on-board new staff regularly
• have a number of codebases that developers dip in and out of