CSS Styling problem

Thanks have created this nice plugin. Everything I need for testimonial can be found here. But the documentation of css styling is still confusing me. I try go to demo site and try the class beach and class tabbed but not working to my page. i use this shortcode in my page:
[strong class=”beach,tabbed” count=”10″ random title thumbnail]
[client]
[field name=”client_name” class=”name”]
[field name=”company_name” url=”company_website” class=”company” new_tab]
[/client]
[/strong]
i put the css for class beach and tabbed in child-theme. But nothing change.
i get the testimonial in white background with white text. Can’t see the text. Please help me? IF possible please put the sticky post about styling in this support forum. May be can help others.

https://www.ads-software.com/plugins/strong-testimonials/