Allow fragment urls in custom properties.

Fixes parcel-bundler/parcel#8125

src/lib.rs

@@ -17994,6 +17994,12 @@ mod tests {
       ".foo{behavior:url(\"Zn9-2q\")}",
       vec![("#foo", "Zn9-2q")],
     );
+
+    dep_test(
+      ".foo { --foo: url(#foo) }",
+      ".foo{--foo:url(\"Zn9-2q\")}",
+      vec![("#foo", "Zn9-2q")],
+    );
   }
 
   #[test]

src/values/url.rs

@@ -94,6 +94,13 @@ impl<'i> Url<'i> {
       return true;
     }
 
+    // If the url starts with '#' we have a fragment URL.
+    // These are resolved relative to the document rather than the CSS file.
+    // https://drafts.csswg.org/css-values-4/#local-urls
+    if url.starts_with('#') {
+      return true;
+    }
+
     // Otherwise, we might have a scheme. These must start with an ascii alpha character.
     // https://url.spec.whatwg.org/#scheme-start-state
     if !url.starts_with(|c| matches!(c, 'a'..='z' | 'A'..='Z')) {