I’m not a CSS expert, and have not used the Divi theme, so can’t really help you directly with regards to that theme.
My plugin actually uses very little CSS to style the tables and other output. Most of the way things are displayed from my plugin is from the default styles of your theme.
My suggestion would be to use the option in my plugin to disable the plugin’s CSS, and then hard code your CSS into your child theme, or wherever Divi lets you put custom CSS.
You can start by copying the relevant CSS from my plugin, which you can find in the assets/css folder. The public side css is the style.css file. You’ll see it’s very small, with the top part styling the tables in a very minimal way, the middle part is mostly for error/success messages, and the bottom part is for styling the divs as tables by default if you have the plugin set to output divs instead of tables.
Copy over the parts you need, and make changes as desired. Most all of the output has custom classes as well, so it should be relatively easy to target just those elements you want to change with some custom CSS. Just inspect the elements in your browser to get the class names for anything you want to change.