Custom background help

Need some help with coding. I need to increase the space between images in a custom background. This is the coding:
if (document.title == “Background testing”){
document.getElementById(“body-wrapper”).style.backgroundImage=”url(‘https://fayettedd.com/wp-content/uploads/2015/10/Eaglet-Background-e1445969633985.jpg’)”;
}

What do I add to make the images farther apart? Any help is appreciated. Thank you.