# Update the environment theme

`PATCH /v1/branding` · permission `branding:write`

Changes the environment theme draft with a JSON merge patch (`application/merge-patch+json`, RFC 7396). A token set to `null` (or a whole group such as `"light": null`) is cleared and inherits again; `"theme": null` clears every token. Only changed tokens are written; a patch that changes nothing keeps the version. Values are checked on write: colors are `#rgb`/`#rrggbb`, `font.size_base` 14-18, `radius.card` 0-24, `radius.control` 0-16, `logo_height` 24-80. `logo`, `favicon` and `background_image` must name an image of that kind uploaded with [Upload a branding asset](/docs/api/management/branding/upload-asset); otherwise the field fails with `asset_not_found`. Contrast is checked on publish.

## Request

| Field | Type | Required | Description |
|---|---|---|---|
| `If-Match` | header | yes | The `ETag` of the draft as last read (`"0"` if never written). Missing: `428`; stale: `412`. |
| `theme` | object \| null | no | Partial `BrandingTheme`; every field and group may be `null`. |

## Response

`200 OK` with the environment draft and its `ETag`. `theme` holds only the tokens that are set; unset tokens inherit from the platform default.

```json
{
  "theme": {"mode": "light", "light": {"color": {"primary": "#0a3d91"}}, "logo_height": 40},
  "css": null,
  "page_template": null,
  "updated_at": "2026-10-05T09:30:00.123456Z"
}
```

## Errors

| HTTP | code | When |
|---|---|---|
| 400 | `unknown_field` | The body has an unknown field or is not a JSON object. |
| 412 | `precondition_failed` | `If-Match` does not match the current version of the draft. |
| 415 | `unsupported_media_type` | The content type is not `application/merge-patch+json`. |
| 422 | `validation_failed` | A token value is invalid (`invalid_value`, `out_of_range`, `unknown_token`); `pointer` names the token, e.g. `/theme/light/color/primary`. |
| 428 | `precondition_required` | The `If-Match` header is missing. |
| 401 | `unauthenticated` | The credential is missing, invalid or revoked. |
| 403 | `insufficient_permissions` | The credential lacks the required permission. |
| 429 | `rate_limited` | The rate limit was exceeded; retry after the `Retry-After` period. |
| 503 | `service_unavailable` | A dependency is temporarily unavailable; retry after the `Retry-After` period. |

## Example

```bash
curl -X PATCH https://api.eu.keenauth.com/v1/branding \
  -H "Authorization: Bearer $KEENAUTH_SECRET_KEY" \
  -H "Content-Type: application/merge-patch+json" \
  -H 'If-Match: "3"' \
  -d '{"theme":{"light":{"color":{"primary":"#0a3d91"}},"radius":null}}'
```