function getRandom(anyArray) {
  var randomNumber = Math.floor(Math.random() * anyArray.length);
  var randomElement = anyArray[randomNumber];
  return randomElement;
}

var pageSettings = {
  red: 200,
  green: 200,
  blue: 200,
  background: [
    'https://pictures.s3.yandex.net/background.jpg',
    'https://pictures.s3.yandex.net/cover-color.jpg',
    'https://pictures.s3.yandex.net/cover-grid.jpg',
    'https://pictures.s3.yandex.net/cover-typo.jpg',
    'https://pictures.s3.yandex.net/cover-wall.jpg'
  ]
};

var bgColor = 'rgb(' + pageSettings.red + ', ' + pageSettings.green + ', ' + pageSettings.blue + ')';
document.body.style.backgroundColor = bgColor;

var header = document.getElementById('main-header');
header.style.backgroundImage = 'url(' + getRandom(pageSettings.background) + ')';
console.log(header);

var i = 0;
console.log(pageSettings.background[i]);
console.log(pageSettings.background[++i]);
console.log(pageSettings.background[++i]);

var cards = document.getElementsByClassName('card');
cards[1].style.color = 'navy';

window.addEventListener('scroll', function () {
  var scrollY = window.pageYOffset;
  var bgValue = 'rgb(' + (pageSettings.red - scrollY / 4) + ', ' + (pageSettings.green - scrollY / 4) + ', ' + (pageSettings.blue - scrollY / 4) + ')';
  console.log(scrollY);
});