[Theme: Divi] Digging Deeper Into Child Themes

Hello, I am digging deeper into WordPress creating a website to mimic another in our company using a different theme. I am using the Divi Theme with a child theme.

I am stuck on a few things that I’m hoping people might help with:

1. In general, do all of the tags that you effect in the child theme have to have a counterpart in the base theme, or can you create new CSS tags? If so how, because Divi seems to erase any new CSS tags I mark text with in WordPress.

2. Along the same vein, I want some text in a paragraph to be in a different color. I tried to create a CSS tag called “redText” and when I Update the page the code is gone. Can I not create my own tags? If not how do I choose the color and change it for the three words I want to display in this specific red?

3. I want the top photograph (which is a background image on a Divi section) to be absolutely at the top, underneath the navigation and logo. How do I apply CSS to that element to give it the absolute position of Top and Left 0? How do you find the name of the element?

4. How do you get rid of the theme’s advertisement on the bottom (Designed by Elegant Themes | Powered by WordPress) of the page?

Answers to any of these questions is much appreciated. Just digging into child themes and love the idea, but definitely some grey areas on my part. Thanks!