text: const buttonPlus = document.querySelector('.btn-success');
  const buttonDash = document.querySelector('.btn-danger');
  
  buttonPlus.addEventListener('click', () => sum(+1));
  buttonDash.addEventListener('click', () => sum(-1));
  
  const outputValue = document.querySelector('output');
  
  function sum (num) {
      const valorAtual = +outputValue.innerHTML + num;
      outputValue.innerHTML = valorAtual;
  
      if (valorAtual > 0) {
          outputValue.classList.add('text-success');
      } else if (valorAtual < 0) {
          outputValue.classList.add('text-danger');
      } else {
          outputValue.classList.remove('text-success');
          outputValue.classList.remove('text-danger');
      }
  }
  