.stringContentIsNotModifiedEvenIfInvalid {
  background: url("@images");
  background: url("$images");
  background: url('/+0PX!/"\a?~^[]{} $%#');
  background: url("/+0PX!/'\a?~^[]{} $%#");
  background: url("whitespace-around-string");
}

.validUnquotedUrls {
  background: url(whitespace-around-string);
  background-image: url(/images/product/simple_product_manager/breadcrumb/chevron_right.png);
  background-image: url(data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAAEAAAABCAQAAAC1HAwCAAAAC0lEQVR42mO4/B8AAqgB0yr7dJgAAAAASUVORK5CYII=);
  background-image: url(data:application/font-woff;charset=utf-8;base64,ThisIsNormalBut/+0ThisIsLowerCased);
  background: url(data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAAEAAAABCAQAAAC1HAwCAAAAC0lEQVR42mO4/B8AAqgB0yr7dJgAAAAASUVORK5CYII=)
    center center no-repeat;
  background: url(data:image/svg+xml,%3Csvg%20xmlns=%22http://www.w3.org/2000/svg%22%20width=%229%22%20height=%229%22%3E%3Cpath%20d=%22M0%203h3%22%20stroke=%22red%22/%3E%3C/svg%3E);
  offset-path: url(#path);
  background: url(data/+0ThisShouldNotBeLowerCased);
  background: url(https://foo/A*3I8oSY6AKRMAAAAAAAAAAABkARQnAQ);
  background: url(https://example.com/some/quite,long,url,with,commas.jpg);
  background: url(http://123.example.com);
}
@import url(https://fonts.googleapis.com/css?family=Roboto:100,300,400,500,700,900&display=swap);

.validUnqotedUrlsThatAreParsedByLess {
  background: url(@foo);
}

.validUnquotedUrlsThatAreParsedBySass {
  background: url($foo);
  background: url($foo+$bar);
  background: url($foo*3);
  background: url($foo/$bar);
}

.invalidUnquotedUrlsButWeParseThemAnyway {
  background: url(--var(foo-bar, #dadce0));
  -fb-sprite: url(fbglyph:cross-outline, fig-white);
}

.number {
  background-image: url(http://123.com);
  background: url(path/to/123.jpg);
  background: url(#123.foo);
  background: no-repeat center/80% url(http://123.com);
  background: no-repeat center/80% url(path/to/123.jpg);
  background: no-repeat center/80% url(#123.foo);
}