Format style for Related Post

Hello, I am using Zemanta’s Related Post plugin and have put the PHP code in the theme for where I want it positioned. Now I just need to format the CSS to be in a white box as per the theme.

Can anyone tell me what I need to paste in the custom css area of the plugin so it can have a box around it with a white background?

This is the related post CSS:

.related_post_title {
}
ul.related_post {
}
ul.related_post li {
}
ul.related_post li a {
}
ul.related_post li img {
}

This my site: http://www.happyindulgencebooks.com/2013/11/26/champion-by-marie-lu-review-beautiful-ending-and-heaps-of-politics/