Debugging CSS problems can be painful. How many times have you had to trawl through thousands of overridden styles to work out the source of your problem? This has led many of our teams to introduce various guidelines such as avoiding cascading and overrides, making styles opt-in and emphasizing thoughtful naming. BEM is a simple CSS naming convention (standing for Block, Element, Modifier) that helps give semantic clarity and structure to your CSS. By using BEM, it becomes much easier to understand which CSS rules are influencing the appearance of an element and, more importantly, the intent of those rules. This approach can be seen as moving the OO lesson of favoring composition over inheritance to the world of CSS.