Add transitions-2.vim

https://www.w3.org/TR/2023/WD-css-transitions-2-20230905/

after/syntax/css/transitions-2.vim

@@ -0,0 +1 @@
+syn match cssFontDescriptor "@\(starting-style\)\>" nextgroup=cssFontDescriptorBlock skipwhite skipnl

test/test.css

@@ -1192,6 +1192,12 @@ view {
 	display: auto;
 }
 
+@starting-style {
+	.transitions-2 {
+		display: auto;
+	}
+}
+
 .typed-om-1 {
 	display: auto;
 }