Coming soon page using Flex/SASS/Media queries and JS

My first challenge which required some JS. This page https://developer.mozilla.org/en-US/docs/Learn/Forms/Form_validation turned out to be very helpful to me with this task :)

One question: I've noticed some CSS issues after uploading the solution and that's the first time I see something like that, probably because that's the first time I used SASS, anyone knows by any chance how to get rid off them?

Any kind of suggestions are very welcome!