handle ` at toplevel

src/stylesheet.rs

@@ -298,6 +298,9 @@ impl<'a> StyleSheetParser<'a> {
                 ',' | '!' => {
                     return Err(("expected \"{\".", self.lexer.next().unwrap().pos()).into());
                 }
+                '`' => {
+                    return Err(("expected selector.", self.lexer.next().unwrap().pos()).into());
+                }
                 _ => todo!("unexpected toplevel token: {:?}", kind),
             };
         }

tests/error.rs

@@ -90,3 +90,7 @@ error!(
     toplevel_exclamation,
     "! {}", "Error: expected \"{\"."
 );
+error!(
+    toplevel_backtick,
+    "` {}", "Error: expected selector."
+);