div { background: url("foo/bar/baz.jpg") } div { background: url('foo/bar/baz.jpg') } div { background: url(foo/bar/baz.jpg) } div { background-image: url(data:image/png;base64,TWFuIGlzIGRpc3=) } div { background-image: url("data:image/png;base64,TWFuIGlzIGRpc3=") } div { background-image: url('data:image/png;base64,TWFuIGlzIGRpc3=') } // https://github.com/highlightjs/highlight.js/issues/3514 div { --custom-background-image-1: url('/appearance/themes/Dark+/image/background (01).jpg'); }