Your welcome, I’m glad you like it!
No – unfortunately there is no option for theming the calendar. The images included in the plug-in are part of two jQuery UI themes bundled with the plug-in. These two themes (based on these trac ticket) are intended to fit in with the two admin ‘skins’ that WordPress provides. One of them is used for the front-end.
If you wanted to over-ride the plug-in provided css – or just prevent it from over-riding a jQuery UI theme – you can to hook onto init (priority > 10) and de-register the style with handle eventorganiser-jquery-ui-style (and optionally re-registering a style with that same handle).
So long as a jQuery theme is loaded – the front-end calendar should be styled accordingly.
No problem, thanks for the info 🙂