show title frame for code blocks with a `data-filename` attribute

src/scripts/filename-transformer.ts

···
 
       if (filename) {
         code.properties.dataFilename = filename;
+
+        code.properties.class +=
+          " relative !pt-[2rem] before:content-[attr(data-filename)] before:absolute before:top-0 before:left-0 before:w-full before:bg-crust before:border-t-2 before:border-l-2 before:border-r-2 before:border-base before:border-solid before:font-bold before:px-4 before:py-1 before:whitespace-nowrap before:overflow-x-auto";
       }
     },
   };