Update docs

Author: blueswen

demo-mkdocs/docs/index.md

@@ -63,7 +63,7 @@ A MkDocs plugin supports for add [Swagger UI](https://github.com/swagger-api/swa
     | oauth2RedirectUrl | String | Default: Absolute URL of "/assets/swagger-ui/oauth2-redirect.html" relative with site_url in mkdocs.yml or document root path on site without site_url, e.g. "[https://blueswen.github.io/mkdocs-swagger-ui-tag/assets/swagger-ui/oauth2-redirect.html](https://blueswen.github.io/mkdocs-swagger-ui-tag/assets/swagger-ui/oauth2-redirect.html)". OAuth redirect URL. |
     | supportedSubmitMethods | Array | Default: All Http Methods. Array=["get", "put", "post", "delete", "options", "head", "patch", "trace"]. List of HTTP methods that have the "Try it out" feature enabled. An empty array disables "Try it out" for all operations. This does not filter the operations from the display. |
     | validatorUrl | String | Default: "none". By default, the validation is disabled. When setting with "https://validator.swagger.io/validator", Swagger UI  attempts to validate specs against swagger.io's online validator in multiple OAS Swagger UI. You can use this parameter to set a different validator URL, for example for locally deployed validators ([Validator Badge](https://github.com/swagger-api/validator-badge)). |
-    | extra_css | Array | Default: []. Extra CSS files included in Swagger UI iframe target html file. |
+    | extra_css | Array | Default: []. Extra CSS files in your `docs_dir` included in Swagger UI iframe target html file. |
 
 ## How it works