All template (views) inside the plugin can be customized and modified in a theme. Post Gallery and Post Gallery PRO will give priority to any copy, of a template, found inside the activated theme.
Copy the templates your want to customize from:
[simple-post-gallery]/assets/views/
Into your theme, at:
[your-theme]/views/
Gallery template
The default gallery layout template is located at:
[simple-post-gallery]/assets/views/plugins/post-gallery/gallery.php
To customize it, paste it in your theme, at:
[your-theme]views/plugins/post-gallery/gallery.php
PRO templates
Only available for Post Gallery PRO *
Similar to the regular plugin, any template (view) from Post Gallery PRO can be customized. Copy the templates you want to customize from:
[simple-post-gallery-pro]/assets/views/
Into your theme, at:
[your-theme]/views/
The PRO layout templates can be found at:
[simple-post-gallery-pro]/assets/views/plugins/post-gallery/