Add selectors-nonelement-1.vim

See also: http://www.w3.org/TR/selectors-nonelement-1/

after/syntax/css/selectors-nonelement-1.vim

@@ -0,0 +1 @@
+syn region cssPseudoClassLang matchgroup=cssPseudoClassId start="::attr(" end=")" oneline

after/syntax/html.vim

@@ -51,3 +51,4 @@ syn include @htmlCss syntax/css/css-writing-modes-3.vim
 syn include @htmlCss syntax/css/html5-elements.vim
 syn include @htmlCss syntax/css/motion-1.vim
 syn include @htmlCss syntax/css/selectors4.vim
+syn include @htmlCss syntax/css/selectors-nonelement-1.vim

test/test.css

@@ -474,6 +474,10 @@
   display: auto;
 }
 
+.selectors-nonelement-1::attr(title) {
+  display: auto;
+}
+
 .shapes {
   shape-outside: margin-box;
   shape-image-threshold: inset(50% 50% 50% 50%);

test/test.html

@@ -521,6 +521,11 @@
 }
 </style>
 <style>
+.selectors-nonelement-1::attr(title) {
+  display: auto;
+}
+</style>
+<style>
 .shapes {
   shape-outside: margin-box;
   shape-image-threshold: inset(50% 50% 50% 50%);