Huddle landing page with curved sections with SASS

Hi guys any feedback, critics, or opinion will be appreciated. Here are a few things I still find difficult to do:

1. I already use sass but my code isn’t simple yet. Do you have any tips about this?
2. I tried to use BEM but I only use block and element. I combine element and modifier in one class
3. Is it better to use rem/em unit rather than pixel unit?
4. Still figuring out how to better use media query especially in sass
5. In this challenge are there any parts that you think are better off using the grid?

Thanks for your responses