Grabbed dndbeyond's source code

```
~/go/bin/sourcemapper -output ddb -jsurl https://media.dndbeyond.com/character-app/static/js/main.90aa78c5.js
```

ddb_main/node_modules/@mui/material/Backdrop/backdropClasses.js

@@ -0,0 +1,7 @@
+import generateUtilityClasses from '@mui/utils/generateUtilityClasses';
+import generateUtilityClass from '@mui/utils/generateUtilityClass';
+export function getBackdropUtilityClass(slot) {
+  return generateUtilityClass('MuiBackdrop', slot);
+}
+const backdropClasses = generateUtilityClasses('MuiBackdrop', ['root', 'invisible']);
+export default backdropClasses;