How do I add this required field to the form?

I want to make this Form. It is not allowed to move to the next steps unless the person fills in the required fields. But I can't activate the "required" feature, even though I added it in HTML. Therefore, I want you to help me and add or activate a required feature to Exact field in that form. But I don't want all the fields, I just want them when I put the word required. And when I add new fields, I want them to work as well. I also want to increase the width of the form to 90% of the total area, while also increasing the size of the progress bar.
here is my full (HTML, CSS and JS): 

https://jsfiddle.net/Maroz/s19q3gnf/3/