text: const sign_in_btn = document.querySelector('#sign-in-btn');
  const sign_up_btn = document.querySelector('#sign-up-btn');
  const container = document.querySelector('.container');
  
  sign_up_btn.addEventListener('click', () => {
    container.classList.add('sign-up-mode');
  });
  
  sign_in_btn.addEventListener('click', () => {
    container.classList.remove('sign-up-mode');
  });
  
  