Explore a comprehensive theory of components in modern web development through this conference talk from CSSconf EU 2019. Delve into the evolving landscape of design systems and front-end code, examining how current tools shape our understanding of components. Learn to define, create, and scale components effectively by developing a checklist of essential factors. Discover how to implement this component theory using available tools, ensuring they are easy to reason about, context-agnostic, and independent. Gain insights into the constant iteration of web development practices and how to adapt to changing technologies. Apply the component checklist to strengthen your approach to modern web design and development, keeping the theory at the forefront of your work.