Add resize-observer-1.vim

https://www.w3.org/TR/2020/WD-resize-observer-1-20200211/

Author: hail2u

after/syntax/css/resize-observer-1.vim

@@ -691,6 +691,10 @@ mask {
   display: avoid-region;
 }
 
+.resize-observer-1 {
+  display: auto;
+}
+
 .rhythm-1 {
   line-height-step: auto;
   block-step-size: auto;