text: const btnSingIn = document.getElementById('singin')
  const btnSingUp = document.getElementById('singup')
  const body = document.querySelector('body')
  
  btnSingIn.addEventListener('click', function() {
      body.className = 'singIn-js'
  })
  btnSingUp.addEventListener('click', function() {
      body.className = 'singUp-js'
  })