This is the BigCommerce Cornerstone reference theme for the Stencil platform, a fully responsive e-commerce storefront. It provides a complete set of pages for product browsing, cart management, checkout, account management, search, and more. The theme is built using Handlebars templates for server-side rendering, JavaScript for client-side interactivity, and SCSS for styling, with a component-based architecture. The JavaScript architecture uses a PageManager base class with page-specific controllers (e.g., Cart, Product, Category) that are dynamically loaded. Key reusable components include a modal with focus trap, collapsible panels with ARIA support, an accessible carousel, faceted search, and form validation utilities. The theme emphasizes accessibility with extensive ARIA attributes and keyboard navigation. The theme is highly configurable via a schema.json that defines hundreds of settings (colors, fonts, layout options) and supports multiple locales through translation files. It integrates with BigCommerce's Stencil CLI and uses modern build tools (Webpack, Babel) alongside legacy ones (Grunt). While primarily a frontend theme, it includes performance optimizations like lazy loading, code splitting, and polyfill-on-demand.