The LayoutBox class is a fundamental C++ component within Chromium’s Blink rendering engine that represents a rectangular CSS box in the layout tree. It serves as the abstract base for most visible web elements, managing core box model geometry such as margins, borders, padding, and content dimensions. By facilitating both logical and physical coordinate systems, the class ensures that elements are positioned correctly regardless of text direction or writing mode. LayoutBox also acts as a critical bridge between the legacy layout system and the modern LayoutNG architecture, caching immutable fragments to enhance performance. Beyond sizing, it handles complex behaviors including overflow management, scrolling mechanics, and CSS fragmentation across columns or pages. Ultimately, this class centralizes the data necessary for subsequent browser stages like painting, hit-testing, and accessibility mapping.