Blend your MCP App with Claude's theme changedconnectors/building/mcp-apps/transparent-theming
Nearest release: v2.1.283, published under an hour after upstream edited the page. Shown because the two are within 24 hours of each other. Nothing here says the release caused the edit.
Upstream edited this page at 25 Sep 2026 18:00 UTC, give or take a minute or two: the time comes from Anthropic’s own sitemap rather than from a commit. This site recorded the change at 28 Sep 2026 22:07 UTC.
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6363Claude passes a [`hostContext`](https://modelcontextprotocol.github.io/ext-apps/api/interfaces/app.McpUiHostContext.html) object to your widget during the [`connect()`](https://modelcontextprotocol.github.io/ext-apps/api/classes/app.App.html#connect) handshake. The fields relevant to theming are:
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65| Field | Contents |
66| :----------------- | :--------------------------------------------------------------------------------------------------------------------------------------------------------- |
67| `theme` | `"light"` or `"dark"` |
65| Field | Contents |
66| :- | :- |
67| `theme` | `"light"` or `"dark"` |
6868| `styles.variables` | CSS custom properties: `--color-background-*`, `--color-text-*`, `--color-border-*`, `--color-ring-*`, `--font-*`, `--border-radius-*`, `--border-width-*` |
69| `styles.css.fonts` | `@font-face` rules for Anthropic Sans, served from `https://assets.claude.ai` |
69| `styles.css.fonts` | `@font-face` rules for Anthropic Sans, served from `https://assets.claude.ai` |
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7171The [Style variables](/docs/connectors/building/mcp-apps/design-guidelines#style-variables) section of the design guidelines lists every variable and its light- and dark-mode value.
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