> ## Documentation Index > Fetch the complete documentation index at: https://lightdash-mintlify-38246967.mintlify.site/llms.txt > Use this file to discover all available pages before exploring further. # Themes > Create shared themes to give your data apps consistent styles, fonts, and instructions. Themes let you define a reusable set of styles and instructions that data apps can pick up. They're a good way to keep apps on-brand across your organization without having to re-prompt the agent for the same look and feel every time. ## What's in a theme A theme is a bundle of resources the agent uses when it builds an app: * **CSS rules.** Instantiated at the root of the app. Global styles are picked up automatically, and class-targeted styles are available for the agent to apply to specific elements based on the theme's instructions. * **Fonts.** Loaded into the app and available to the agent. * **Images.** Logos, imagery intended to be used in the app, design inspiration, or examples of component styles you'd like the agent to follow. The agent tries to guess each image's intent from its name and content, but you can be explicit in the instructions. * **`skill.md`.** Free-form instructions for the agent on how to use the theme. This can describe a vibe, specific interactions, or tell the agent exactly how to use the other resources in the theme. * **Extra instructions.** A free-text field on the theme itself, edited inline from the theme detail panel. Useful for quick tweaks you don't want to manage as a file. See [Extra instructions](#extra-instructions) below. The quality of a theme depends largely on the specificity of the instructions in `skill.md` and the extra instructions field. The more concretely you describe how the agent should use the CSS, fonts, and images - and what the app should feel like - the more consistent your results will be. ### Size limit A theme's files are streamed into the app sandbox. To keep things fast and predictable, themes have a hard limit of **100 MB total across all uploaded assets** (fonts, images, and instruction files combined). Individual files are capped at 10 MB. The cap is on aggregate bytes, not file count — a theme with many small text files is cheap, but a handful of large images can blow past it. Compress or downscale image assets, or split them into a smaller curated set, if you're near the limit. ## Extra instructions Each theme has an **Extra instructions** field that you can edit directly from the theme detail panel in **Settings → Themes**. These instructions are passed to the agent alongside any uploaded instruction markdown files when an app is built with the theme. Use extra instructions for: * Quick guidance you want to iterate on without uploading or re-uploading a file. * Overrides or additions that complement a stable `skill.md`. * Short, focused directives — for example, capitalization rules, layout preferences, or tone. Example: ```text Extra instructions theme={null} Use sentence case for all headings. Prefer dense layouts over generous whitespace. Always show the company logo in the top-left corner of the app. ``` Leave the field blank to disable it — empty values are ignored at build time. ## Creating a theme You create and manage themes from the **Themes** page in **Settings**. Bootstrapping a theme with an agent (for example, asking an LLM to draft CSS rules and a `skill.md` against these guidelines) is a quick way to get a usable first version. From there, iterate on the instructions until the agent produces apps that match what you have in mind. ## Manage themes as code You can download, version, review, and upload themes through the same organization content-as-code workflow used for custom roles, users, and groups: ```bash theme={null} lightdash download --organization # Edit or add lightdash/themes// lightdash upload --organization ``` This lets you move an existing UI-created theme into version control or create a theme locally. Organization download includes every theme and writes each one under its immutable slug: ```text theme={null} lightdash/ themes/ acme-brand/ lightdash-theme.yml css/ theme.css fonts/ acme-sans.woff2 images/ logo.svg instructions/ skill.md ``` The directory name must exactly match the manifest's `slug`. Every manifest field is required; use `null` for an empty description or extra instructions: ```yaml lightdash/themes/acme-brand/lightdash-theme.yml theme={null} codeVersion: 1 slug: acme-brand name: Acme Brand description: Brand theme for customer-facing data apps extraInstructions: |- Use the horizontal logo in page headers. Keep data-dense tables compact. ``` To create a new theme locally, choose a new lowercase, hyphenated slug, create this manifest and any asset folders you need, then run `lightdash upload --organization`. Upload creates or updates the theme by manifest slug. Treat the slug as immutable; change `name` when you only want to rename the theme for display. Organization mode has no theme-only selector. Before uploading, review custom roles, users, and groups under the same `lightdash/` directory as well as your themes. ### Files and validation The CLI validates every local theme before changing any organization resource. A theme package accepts: * `.css` files under `css/` * `.woff`, `.woff2`, `.ttf`, and `.otf` files under `fonts/` * `.png`, `.jpg`, `.jpeg`, `.gif`, `.webp`, and `.svg` files under `images/` * Markdown files under `instructions/` Files must live directly inside one of these folders. Nested folders, symlinks, unknown paths, unsafe filenames, unsupported file types, empty files, and files whose contents don't match their extension are rejected. The manifest is limited to 64 KiB, each asset to 10 MB, all assets combined to 100 MB, and the complete uncompressed package to 110 MB. Don't commit or upload restricted Apple system-font binaries such as SF-family or New York fonts. Use a system font stack instead: ```css theme={null} font-family: system-ui, -apple-system, BlinkMacSystemFont, "Segoe UI", sans-serif; ``` ### Synchronization behavior * A successful download replaces the complete local `themes/` directory with the remote theme set. If any theme cannot be downloaded or validated, your previous local themes are preserved. * Upload preflights every local theme before applying custom roles, users, groups, or themes. One invalid theme prevents all organization changes in that run. * An existing slug is updated, a new slug is created, and a theme whose manifest and files already match is skipped as unchanged. * A missing or empty local `themes/` directory is a no-op. Removing one local theme directory does not delete the remote theme. * Upload preserves each theme's UUID and whether it is the organization default. Set the default or delete a theme in the Lightdash UI. * Each theme import is atomic, but a multi-theme upload is not one transaction. If a later import fails, themes that completed earlier remain applied and the CLI reports the partial failure. There is no standalone `lightdash themes` command, theme-specific `--only` flag, or local theme preview. If an organization theme endpoint returns `404`, check that the Lightdash CLI and server versions both support theme packages. ### Evaluate your changes Uploading proves the package is valid, but it doesn't rebuild or restyle existing data app versions. To see whether you like a theme, select it when generating a new data app or apply it to an existing app from the theme picker above the prompt. Lightdash creates a new app version that you can compare with the previous version. If you edit themes with an AI coding agent, install or update the [Lightdash agent skills](/guides/developer/agent-skills). The existing `developing-in-lightdash` skill teaches the agent this package format and the safe organization download/upload workflow. The agent can verify the CLI round trip without browser access; you still evaluate the generated app visually in Lightdash. ## Setting a default theme You can mark one theme as the default for your organization. New data apps will use the default theme unless you pick a different one. ## Using a theme in a data app When you create a new data app, you can choose which theme to apply. The agent will use the theme's CSS, fonts, images, and `skill.md` instructions as part of the context for the build.