If you want to edit the style of your Divi theme much like the sites in the Divi showcase, then the easiest way is via custom CSS, which is added to your Divi theme options panel under custom css, or into a .styles.css file within your Divi child theme.
But, if you don’t know CSS well or know specifically what CSS code that you need to add, then there is another, very easy option.
CSSHERO is a plugin that allows you to edit your CSS in real-time, in the browser window without having to know any CSS code at all. Just click the element you want to edit and use the simple click/drag/slide tools to change how it looks. The CSS is all edited for you! Easy, fast and effective way of customising your Divi theme without having to know how the CSS code is working behind the scenes.
Pick up your copy of CSS Hero here.