diff --git a/after/syntax/css/position-4.vim b/after/syntax/css/position-4.vim
new file mode 100644
index 0000000..eeb1338
--- /dev/null
+++ b/after/syntax/css/position-4.vim
@@ -0,0 +1,2 @@
+syn keyword cssFontProp contained overlay
+syn keyword cssPseudoClassId contained backdrop
diff --git a/test/test.css b/test/test.css
index 4ee519a..6f0028c 100644
--- a/test/test.css
+++ b/test/test.css
@@ -879,6 +879,10 @@ mask {
   inset: auto;
 }
 
+.position-4::backdrop {
+  overlay: auto;
+}
+
 .properties-values-api-1 {
   syntax: auto;
   inherits: auto;