[madeas]

настроил.

var back = document.querySelector("#back"),
  x = document.querySelector("#posX"),
  y = document.querySelector('#posY'),
  so = document.querySelector('#sizeOne'),
  st = document.querySelector('#sizeTwo'),
  si = document.querySelector('#sizeIn');
(style = () => {
  back.style.backgroundImage = 'url(' + document.querySelector("#bgImage").value + ') ';
  back.style.backgroundSize = so.checked ? 'cover' : st.checked ? 'contain' : si.value + 'px';
  back.style.backgroundRepeat = document.querySelector('[name="repeat"]:checked').parentNode.textContent;
  back.style.backgroundPosition = y.value + '%' + x.value + '%';
})();
document.querySelectorAll('input').forEach(el => el.oninput = style);