Base Apparel coming soon page (Mobile-First)

Hello everyone, This is my solution for this challenge.

This was my first time working with forms in a piratical way. I spent a lot of time making it responsive, as the picture on desktop was creating some problem while changing the width of the screen. I fixed it by applying min-max width for the picture. The HTML structure I've used here works, and I'm aware that its not correct, as i can't use it while dealing with multiple inputs. I was having doubts about it so i watched a video, and i understand it now.

I'm still writing pure CSS. I'm kinda feeling lost, i don't know if i should use SASS, bootstrap, or if i should make my own custom classes for different purpose and apply these multiple classes to the element for styling. I know how bootstrap works, but I'm avoiding it because i fear that by using it i might be able to make good and responsive websites but i won't really understand how these CSS properties work and react to one another.
and about Sass, i used it and i was having trouble with organizing my sass. I read some articles but then i was like "okay so im i supposed to write the layouts in one module and not define the typography, color and stuff here, and then select these elements again in another module to define the typography and stuff??" It seems time consuming, and i don't know if this is really how im suppose to do it. I would really appreciate some help with this.

Thanks!