Add css-overflow-4.vim

See also: http://www.w3.org/TR/2017/WD-css-overflow-4-20170613/

after/syntax/css/css-overflow-4.vim

@@ -0,0 +1,4 @@
+syn keyword cssFontProp contained continue
+syn match cssFontProp contained "\<scrollbar-gutter\>"
+syn keyword cssFontAttr contained stable force overflow paginate fragments
+syn region cssPseudoClassLang matchgroup=cssPseudoClassId start=":\(nth-fragment\)(" end=")" oneline

after/syntax/html.vim

@@ -23,6 +23,7 @@ syn include @htmlCss syntax/css/css-lists-3.vim
 syn include @htmlCss syntax/css/css-logical-1.vim
 syn include @htmlCss syntax/css/css-masking-1.vim
 syn include @htmlCss syntax/css/css-overflow-3.vim
+syn include @htmlCss syntax/css/css-overflow-4.vim
 syn include @htmlCss syntax/css/css-page-floats-3.vim
 syn include @htmlCss syntax/css/css-paint-api-1.vim
 syn include @htmlCss syntax/css/css-position-3.vim

test/test.css

@@ -504,6 +504,14 @@
   max-lines: auto;
 }
 
+.overflow-4::nth-fragment(1) {
+  scrollbar-gutter: stable;
+  continue: force;
+  display: overflow;
+  display: paginate;
+  display: fragments;
+}
+
 .page {
   display: avoid-page;
   display: page;

test/test.html

@@ -553,6 +553,15 @@
 }
 </style>
 <style>
+.overflow-4::nth-fragment(1) {
+  scrollbar-gutter: stable;
+  continue: force;
+  display: overflow;
+  display: paginate;
+  display: fragments;
+}
+</style>
+<style>
 .page {
   display: avoid-page;
   display: page;