Beginners CSS trouble

Hi, I’m a beginner with website building and in the process of building a website for my first website for my aunt. I’m building a directory of posts on the site and am trying to edit the appearance of a post list plugin, but I cannot work out how to access the CSS for this plugin. This is the plug in I am using: http://ww.wp.xz.cn/plugins/category-post-shortcode/other_notes/
and this is how it looks on the page at the moment:
http://www.katrinaallen.co.uk/articles/tennisreal-tennissport/

Could anyone tell me how I would go about editing the appearance of this directory?