The document discusses building a design system using Polymer web components. It provides an overview of the key aspects of web components, including custom elements, HTML imports, templates, shadow DOM, and how they enable encapsulation and reuse of UI elements. It then demonstrates how to build a simple custom element in Polymer, including defining the element class, template, and styles. The presentation emphasizes how Polymer and web components help manage styles and build reusable, encapsulated UI components for design systems.