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Block Element Modifier is the latest industry best practice for writing CSS. It is a set of rules on how to name and use more CSS classes. BEM is a guideline, not a piece of technology or a new framework, so you don’t have to update your CV. The class block refers to the parent container of various related elements, while the class block__element refers to its contents. These contents may be of different CSS stylings hence, to differentiate them you may attach a modifier to its class.