Gatsby, a versatile platform for building various websites such as blogs and e-commerce frontends, introduces themes to enhance reusability and scalability. At its core, a Gatsby site is governed by a single configuration file, gatsby-config.js, which orchestrates plugins and site metadata. While starters allow developers to quickly scaffold new projects, they lack the update flexibility offered by themes. Themes enable portions of the gatsby-config to be reused across different projects, allowing for seamless updates and customization without overwriting existing modifications. This feature supports the distribution of functionalities as npm packages and accommodates branding customization through parameterized configurations. Themes can be combined with site-specific configurations, providing a base for reusable and upgradable designs that solve a variety of use cases. Gatsby is exploring advanced theming features like sub-theming and component shadowing to allow more granular overrides, with ongoing development supported by the Gatsby community.