What is Style guide?

A style guide is a document that provides guidelines for the way your brand should be presented from both a graphic and language perspective. The purpose of a style guide is to make sure that multiple contributors create in a clear and cohesive way that reflects the corporate style and ensures brand consistency with everything from design to writing

There are few types:

• Visual style guide — For maintaining consistency in the visual design.
• Editorial Style Guide - Rules for company voice
• UI Kit - Visual guide for maintaining components, system and communication with developers

Some tools that I frequently use: KSS, XD, CSS, Fontastic, Flaticon, Google fonts, Adobe creative suite.