Correctly print whitespace when no params in at rule

src/css.rs

@@ -134,7 +134,11 @@ impl Css {
                 }
                 Toplevel::AtRule(r) => match r {
                     AtRule::Unknown(u) => {
+                        if u.params.is_empty() {
+                            writeln!(buf, "{}@{} {{", padding, u.name)?;
+                        } else {
                             writeln!(buf, "{}@{} {} {{", padding, u.name, u.params)?;
+                        }
                         Css::from_stylesheet(StyleSheet::from_stmts(u.body.clone()))
                             .pretty_print(buf, nesting + 1)
                             .unwrap();

tests/media.rs

@@ -7,6 +7,10 @@ test!(
     basic_toplevel,
     "@media foo {\n  a {\n    color: red;\n  }\n}\n"
 );
+test!(
+    toplevel_no_params,
+    "@media {\n  a {\n    color: red;\n  }\n}\n"
+);
 test!(
     basic_nested,
     "a {\n  @media foo {\n  color: red;\n  }\n}\n",