function fadeIn() {
  var white = document.getElementById('light');
  var black = document.getElementById('fade');
  white.style.display = 'block';
  black.style.display = 'block';
}

function fadeOut() {
  var white = document.getElementById('light');
  var black = document.getElementById('fade');
  white.style.display = 'none';
  black.style.display = 'none';
}