We are assuming that you have downloaded the Divi Theme and/or we have installed it for you.
We will have set up the username and password of the theme so you can get updates.
The Divi Plugin can be found on the Dashboard down the bottom. Click on this and click on Theme Options.

Under Theme Options there are a lot of areas to contend with.
We will start with the Theme Options.

Divi – Theme Options

In this area, the first tab is General.
At the very bottom we have Custom CSS.

Theme Options -> General ->Custom CSS

Here are some Custom CSS snippets that we work with to improve the look and feel of a website, then Divi does not yet have these specific Controls.

This creates padding between elements of a menu of 30px.
Change to what you want.

.et-l--header .et-menu-nav>ul>li {
padding: 0 30px!important;
}

Unlike Pages, there is not a Page Setup feature to turn the Post Content Block transparent. Instead, this does it globally.

.single-post #main-content {
background-color: transparent;
}

I think I have found other ways to do this, but I had an issue when I could not get the background to the desired colour.
This did it for me!

main-content {
background-color: #0e1435!important;
}

Like above, I want to make sure the desired colour.

.free-archive-wrapper {
background-color: #0e1435!important;
}

Other Lessons on Divi: