[CSS] Add support for at-scope rule

Resolves sublimehq#3867

This commit implements support for @scope rules.

see: https://developer.mozilla.org/en-US/docs/Web/CSS/@scope

Author: DeathAxe

CSS/CSS.sublime-syntax

@@ -387,6 +387,7 @@ contexts:
     - include: at-page
     - include: at-page-margin
     - include: at-property
+    - include: at-scope
     - include: at-scroll-timeline
     - include: at-other
 
@@ -406,6 +407,7 @@ contexts:
     - include: at-page
     - include: at-page-margin
     - include: at-property
+    - include: at-scope
     - include: at-scroll-timeline
     - include: at-other
 
@@ -892,6 +894,32 @@ contexts:
     - include: comments
     - include: else-pop
 
+###[ SCROPE AT-RULE ]##########################################################
+
+  at-scope:
+    - match: (@)(?i:scope){{break}}
+      scope: keyword.control.directive.css
+      captures:
+        1: punctuation.definition.keyword.css
+      push: at-scope-selector
+
+  at-scope-selector:
+    - meta_scope: meta.at-rule.scope.css
+    - match: \(
+      scope: punctuation.section.group.begin.css
+      push: at-scope-selector-group-body
+    - match: to{{break}}
+      scope: keyword.other.css
+    - include: else-pop
+
+  at-scope-selector-group-body:
+    - meta_scope: meta.group.css
+    - meta_content_scope: meta.selector.css
+    - match: \)
+      scope: punctuation.section.group.end.css
+      pop: 1
+    - include: selector-body
+
 ###[ SCROLL-TIMELINE AT-RULE ]#################################################
 
   # @scroll-timeline

CSS/syntax_test_css.css

@@ -1554,6 +1554,53 @@
 /*               ^ punctuation.terminator.rule.css */
 }
 
+    @scope
+/*  ^^^^^^ meta.at-rule.scope.css keyword.control.directive.css */
+
+    @scope to ;
+/*  ^^^^^^^^^^ meta.at-rule.scope.css  */
+/*  ^^^^^^ keyword.control.directive.css */
+/*         ^^ keyword.other.css */
+/*            ^ punctuation.terminator.rule.css */
+
+    @scope () to () {}
+/*  ^^^^^^^^^^^^^^^^ meta.at-rule.scope.css */
+/*         ^^ meta.group.css */
+/*               ^^ meta.group.css */
+/*                  ^^ meta.property-list.css meta.block.css */
+/*  ^ punctuation.definition.keyword.css */
+/*  ^^^^^^ keyword.control.directive.css */
+/*         ^ punctuation.section.group.begin.css */
+/*          ^ punctuation.section.group.end.css */
+/*            ^^ keyword.other.css */
+/*               ^ punctuation.section.group.begin.css */
+/*                ^ punctuation.section.group.end.css */
+/*                  ^ punctuation.section.block.begin.css */
+/*                   ^ punctuation.section.block.end.css */
+
+    @scope (.class) to (.limit > *) {}
+/*  ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ meta.at-rule.scope.css */
+/*         ^ meta.group.css - meta.selector */
+/*          ^^^^^^ meta.at-rule.scope.css meta.group.css meta.selector.css */
+/*                ^ meta.group.css - meta.selector */
+/*                     ^ meta.group.css - meta.selector */
+/*                      ^^^^^^^^^^ meta.at-rule.scope.css meta.group.css meta.selector.css */
+/*                                ^ meta.group.css - meta.selector */
+/*                                  ^^ meta.property-list.css meta.block.css */
+/*  ^ punctuation.definition.keyword.css */
+/*  ^^^^^^ keyword.control.directive.css */
+/*         ^ punctuation.section.group.begin.css */
+/*          ^^^^^^ entity.other.attribute-name.class.css */
+/*                ^ punctuation.section.group.end.css */
+/*                  ^^ keyword.other.css */
+/*                     ^ punctuation.section.group.begin.css */
+/*                      ^^^^^^ entity.other.attribute-name.class.css */
+/*                             ^ keyword.operator.combinator.css */
+/*                               ^ constant.other.wildcard.asterisk.css */
+/*                                ^ punctuation.section.group.end.css */
+/*                                  ^ punctuation.section.block.begin.css */
+/*                                   ^ punctuation.section.block.end.css */
+
     @scroll-timeline
 /*  ^^^^^^^^^^^^^^^^^ meta.at-rule.scroll-timeline.css */
 /*  ^ keyword.control.directive.css punctuation.definition.keyword.css */