Sure, can you please link me to a page where the plugin is active? The theme stylesheet is most likely overriding the plugin styles. With some custom CSS is definitely fixable.
One thing you should try first though. Go to the Compatibility Settings submenu under the Related Posts Pro menu, and turn on the first option, Load inline stylesheets?, that might change something on the layout: https://i.imgur.com/8kJKD6w.pngBest,
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