Hi,
You can use your own custom CSS style, here you’ll find the base style included in the plugin: NLP-DefaultStyle.css, you’re free to tweak rules to suit your needs.
This is the list of CSS classes and nodes when using Unordered Lists (by default): nlposts-ulist-nodes
And this one when using blocks: nlposts-block-nodes
Thumbnail images css styles are set by these rules:
Unordered Lists: .nlposts-ulist-container .nlposts-ulist-thumbnail-litem a > img
Ordered Lists: .nlposts-olist-container .nlposts-olist-thumbnail-litem a > img
Blocks: .nlposts-block-container .nlposts-block-thumbnail-litem a > img
Once you’re done with your custom style, save it to your active WordPress theme folder. Name it the way you want: nlp-mycustomstyle.css then set the css_style parameter, like this:
[nlposts css_style=nlp-mycustomstyle]
Please note there is no .css, this parameter works with filenames only.
Hope this helps, cheers.