diff --git a/after/syntax/css/resize-observer-1.vim b/after/syntax/css/resize-observer-1.vim
new file mode 100644
index 0000000..e69de29
diff --git a/test/test.css b/test/test.css
index 1ea6eca..e6d7c7a 100644
--- a/test/test.css
+++ b/test/test.css
@@ -691,6 +691,10 @@ mask {
   display: avoid-region;
 }
 
+.resize-observer-1 {
+  display: auto;
+}
+
 .rhythm-1 {
   line-height-step: auto;
   block-step-size: auto;