Any CSS guides?

Check out the folowing link https://www.metaphorcreations.com/article/css-apply-create-ticker-resembles-top-ticker-dittynewsticker-com/ to style a ticker similar to the scrolling ticker at the top of https://www.dittynewsticker.com/ditty-news-ticker/

To add a max width you could use the following css:

#mtphr-dnt-??? {
  max-width: 600px;
}

The ticker will continue to be responsive at smaller dimensions.

Great, many thanks!

I finally used a % for width instead of a fixed one in pixels and used
.mtphr-dnt-wrapper only at the page where the shortcode is used. Seems to work quite nicely.

Good to hear!

Nice plugin, congrats!