The Thumbnail Title & Description Text frame is used for styling the thumbnails and descriptions on the gallery thumbnails.
What can be styled with the text frame?
Spacing cannot be styled directly on the text frame, it can be styled only in the widget options panel
Using multiple galleries
When using multiple galleries on one page or if you change the name of your gallery within the Container widget, please be sure to change the Tooltip name of the Text Frame within the Hyperlinks > Tooltip panel.
if the gallery name is "Gallery1", the tooltip name on the title and description text panel in Muse must be Thumbnail_Gallery1
Likewise, if you have another gallery names Gallery2, you should change the Tooltip name for its text frame to Thumbnail_Gallery2