Component with sign up form made with HTML, CSS and JavaScript

Another form component, all the designing and form element part was easy to make, I had a little challenge making those error messages if text fields was left blank, As I am a beginner to JavaScript I made it to work on the first name field but I had a difficulty putting it on the rest of the text field. And putting that error icon inside text field was easy but I couldn't make it to show with the error. So, could you suggest some easy ways to make it work using less complicated code in JavaScript.