Sync svelte docs (sveltejs#1531)

sync svelte docs

Co-authored-by: svelte-docs-bot[bot] <196124396+svelte-docs-bot[bot]@users.noreply.github.com>

Author: 2 people

apps/svelte.dev/content/docs/svelte/98-reference/21-svelte-compiler.md

@@ -790,7 +790,7 @@ cssHash?: CssHashGetter;
 </div>
 
 A function that takes a `{ hash, css, name, filename }` argument and returns the string that is used as a classname for scoped CSS.
-It defaults to returning `svelte-${hash(css)}`.
+It defaults to returning `svelte-${hash(filename ?? css)}`.
 
 </div>
 </div>