Naming conventions used by developers to better manage CSS which lacks built-in scoping mechanism.
BEM is a methodology, a naming system, and a suite of related tools. Created by the team at Yandex. Its name is an abbreviation of the key elements of the methodology — Block, Element and Modifier.
Atomic CSS is the approach to CSS architecture that favors small, single-purpose classes with names based on visual function.
Object oriented CSS was proposed by web developer Nicole Sullivan in 2008. Her goal was to make dynamic CSS more manageable by applying the principles of object oriented design popularized by programming languages such as Java and Ruby.
SMACSS stands for Scalable and Modular Architecture for CSS, is more like a style guide to document a consistent approach to site development when using CSS.
A sane, scalable, managed CSS architecture from CSS Wizardry
Multilayer CSS organization methodology is a guideline to structure your CSS. This style of code writing suggests splitting styles into several parts, called layers like foundation, base, project and cosmetic.
Attribute Modules (AM) is a technique for using HTML attributes and their values rather than classes for styling elements
Flat hierarchy of selectors, Utility styles, Name-spaced components. This approach imposes quite a few requirements on the project and the code structure, it only establishes the preferred form of recording selectors and the way they are used in the markup