Building a Custom Theme with CSS

Hello Qualtrics friends. I am working on a pet project where I use a 'survey' as a sort of home page / landing page to distribute information and host various forms (in the form of separate surveys). I am using Qualtrics because 1) it is a tool we are trying to promote within our Org. and 2) web development skills are lacking (to say the least) in our Org. and 3) I am knowledgeable enough in Qaultrics that I think I can build out a fairly cohesive experience.

The area I am having the most trouble is using CSS to tweak the theme in order to make the web page feel right. By finding random articles online I have been able to piece together a very rough example of what I am concepting, but I need help with some of the nuts and bolts as my coding skills have (thus far) only gone as far as needed in order to accomplish a goal, and never with any formal training.

I have 2 questions to this community.
1. Does anyone have good resources for understanding the foundation of CSS? I find W3 school is good if I know the exact challenge I am trying to face and Codecademy is good for general education. Just curious of other sources.
2. Would anyone be willing to message back and forth on how to do very specific things within the Qualtrics platform. Some examples would be:
* Adjust padding between questions.
* Adjust the max-width of the question area. (I think Qualtrics calls this .skin .skininner)

Everyone should feel free to check it out (again very rough) Pet Project Landing Page. What you see is my adjustments from the Blank (for styling) theme Qualtrics provides. I will probably keep this project open while I tweak things, so feel free to see the evolution of the pet project.

Also, I know that I can do this all by having Qualtrics build me a custom theme, and to be honest I may end up doing that, but I am really using this project as a way to improve my skills.