Contact form using HTML, CSS and JS

What are you most proud of, and what would you do differently next time?

I am proud that I have taken a lot reference to do the JavaScript solution and all of it is my creation. I am confident that I am improving in the logic making. My code is really long. I want to know how to use a shorter code that is more optimized

What challenges did you encounter, and how did you overcome them?

Challenges I encountered is figuring out how each field when left empty must show the mandotry field error message individually, I had brainstormed and created a logic on my own to create individual flag for each field.