Finding your thumbnail selector
This is part of the initial setup in the app settings page. The app needs this as a hint on where to do it's magic.
This part can be a bit tricky and knowing some HTML basics will definitely be helpful. If you need help with this just let uns know.
To identify the relevant element for your page, you can inspect the elements with Chrome/Firefox (right click on a thumbnail and inspect or hit F12).
Look out for the element (an element in HTML is for example a <div>...</div>) that surrounds your thumbnails (NOT the main image), the one which is the first common ancestor to your thumbnail images.
The following example might give you an Idea what you are looking for.
This element will have a class or an ID which you should copy over to the settings area. In case it is a class, please add a dot before the name, e.g.:
If the container has an ID, you should add a hashtag, e.g.:
The default setting for the thumbnail container is: