.foo {
	background: url('../images/green.png');
}

.bar {
	background: url(green.png);
}

.url-modifier {
	background: url("../images/green.png" something);
}

.fragment {
	background: url("../images/green.png#foo");
}

.search {
	background: url("../images/green.png?foo=bar");
}
