Right now the CSS says something like this:
#wallpaper {
background-image: url('/s3/theme_images/1658221.jpg?1414962405');
}
So a media query basically lets you pick different CSS depending on window size. So try something like this to make a different image appear if you have a narrower screen:
@media (max-width: 1024px) {
#wallpaper {
background-image: url('some-other-image-for-smaller-resolution');
}
}
Add that in and you should see the image disappear as the window narrows down to 1024px wide, simple!
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