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HTML

              
                <div class="m-4">
  <p id="success" class="bg-green-300 p-4 hidden">🎉 Form submitted successfully!</p>
  <form class="my-4 flex flex-col gap-3 align-self-end max-w-sm rounded-lg p-4 bg-stone-200" novalidate>
      <label for="password">Password</label>
      <input id="password" type="password" required class="bg-slate-50">
      <p id="password-error" class="error text-red-800"></p>
    
      <label for="confirmPassword">Confirm Password</label>
      <input id="confirmPassword" type="password" required class="bg-slate-50">
      <p id="confirmPassword-error" class="error text-red-800"></p>
    <button class="self-end bg-cyan-800 text-white px-4 py-1">Submit</button>
  </form>
</div> 
              
            
!

CSS

              
                p:empty { 
  display: none;
}
              
            
!

JS

              
                const form = document.querySelector('form');
const error = document.querySelector('.error');
const input = document.querySelector('input');
const success = document.querySelector('#success');

const inputs = {
  password: document.querySelector('#password'),
  confirmPassword: document.querySelector('#confirmPassword')
}

const errorMessages = {
  password: document.querySelector('#password-error'),
  confirmPassword: document.querySelector('#confirmPassword-error')
};

form.addEventListener('submit', event => {
  success.classList.add('hidden');
  
  // Stop the form submission so we don't leave CodePen!
  event.preventDefault();
  
  errorMessages.password.textContent = '';
  errorMessages.confirmPassword.textContent = '';
  
  validatePasswordMatch();
  
  if (form.checkValidity()) {
    success.classList.remove('hidden');    
  }
});

function handleInvalid(event) {
  errorMessages[event.target.id].textContent = event.target.validationMessage;
}

function validatePasswordMatch() {
  if (inputs.password.value !== inputs.confirmPassword.value) {
    inputs.confirmPassword.setCustomValidity('Passwords do not match');
  } else {
    inputs.confirmPassword.setCustomValidity('');
    errorMessages.confirmPassword.textContent = '';
  }
}

function handleInput(event) {
  errorMessages[event.target.id].textContent = '';
  event.target.checkValidity();
  
  // Revalidate the password match if there's been an error
  if (errorMessages.confirmPassword.textContent) {
    validatePasswordMatch();
  }
}

inputs.password.addEventListener('invalid', handleInvalid);
inputs.confirmPassword.addEventListener('invalid', handleInvalid);

inputs.password.addEventListener('input', handleInput);
inputs.confirmPassword.addEventListener('input', handleInput);

              
            
!
999px

Console