JSFiddle - React, Tailwind, and code Playground

HTML

<form id="theForm">
      <label for="name" required>Please enter your name</label>
      <input type="text" id="name"><br><br>
      <label for="age" required>Please enter your age</label>
      <input type="text" id="age"><br><br>
      <label for="colour">Please select a colour: </label>
      <select id="colour" required>
        <option value="Yellow">Yellow</option>
        <option value="Blue">Blue</option>
        <option value="Red">Red</option>
        <option value="Green">Green</option>
      </select><br><br>
      <label for="">Select your difficulty:</label>
      <select id="difficulty">
        <option value="1">1. Easy</option>
        <option value="2">2. Medium</option>
        <option value="3">3. Hard</option>
      </select>
      <br><br>
      <input type="submit" />
    </form>

CSS

.hide {
  visibility: hidden;
}

JavaScript

var theForm = document.getElementById("theForm");
theForm.addEventListener('submit', function(e) {
  e.preventDefault();
  this.classList.add("hide");
});