var pageSettings = {
  red: 200,
  green: 200,
  blue: 200,
  background: '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');
console.log(header);