We have created an HTML App stream template that shows how elements and classnames should be used in order to maintain a consistent UI across HootSuite: https://hootsuite.s3.amazonaws.com/jsapi/0-5/app_stream_template.html.
The auto-loaded stylesheets for the different themes are located at:
To further assist you with the functional aspects of an App we have also created a Demo App for you to download. It addresses common issues such as unobtrusive stream refresh handling and 3rd party account integration.
The Demo App works out of the box, just place it on your webserver and point your app settings (on hootsuite.com/developers) to it - instructions are included.
HootSuite Demo App (57KB zip)