Skilled e-learning landing page

Hey everyone, couple of things I'd appreciate feedback on.

1. For the life of me I can't figure out why the navy blue "Get Started" Button at the top right of the page isn't working properly when I hover it. All of they styles are taking effect, except for the hover affect. Can't figure out why...

2. For this project I felt like I was fighting with the css a lot when making the page responsive. For instance when you shrink it down the logo and button in the "menu" at the top of the page are responsive and will shrink/move as the page adjusts but they don't do this anymore once you get to the 650px screen width. (This is where I have a media query but I don't know what I did that made it stop being responsive.) What am I doing that is making it so I have to fight with the CSS, rather than naturally being responsive?

3. Lastly I just realized this as I was about to hit submit, when you inspect and go to the responsive dimensions, you can scroll to the right past where the image was supposed to be cut off. How do I fix that?

Thanks!