Can anyone help with css for styles

Is there anyone who could let me know how or where to find css code to change the default style?

You can customise some things via the plugin settings. Any other customisation you need to do in your theme css. It is completely flexible and you can make the catalogue however you want.

Also is it possible to have the gallery image without the thumbnail in the corner?

I think you are talking about the thumbnail for the product gallery on product detail page template right? If so, you can add three product images, and the idea is that the thumbnails show larger to the right when you click on them. If you don’t want this functionality you could fork the plugin and remove the functionality, or you could simply use css to hide the div classes you don’t want to display.