my solution using css, BEM, DOM, and javascript

I think the javascript validation is the worst part. How can I make it more simple? In addition i think the code has to many DOM elements. How can i use less of them? About the Success HTML code hardcoded in one variable, I know that is not the best practice, but i want to finish. About the BEM styles, I feels great, i think is good enought. I apreciate your comments about this project, mostly about the javascript code! Thanks in advance.