[TASK] Use native type declarations in Document (#1137)

Part of #811

Author: oliverklee

CHANGELOG.md

@@ -32,7 +32,7 @@ Please also have a look at our
 - Make all non-private properties `@internal` (#886)
 - Use more native type declarations and strict mode
   (#641, #772, #774, #778, #804, #841, #873, #875, #891, #922, #923, #933, #958,
-  #964, #967, #1000, #1044, #1134, #1139)
+  #964, #967, #1000, #1044, #1134, #1137, #1139)
 - Add visibility to all class/interface constants (#469)
 
 ### Deprecated

src/CSSList/Document.php

@@ -42,7 +42,7 @@ public static function parse(ParserState $parserState): Document
      *
      * @see RuleSet->getRules()
      */
-    public function getAllValues($element = null, $searchInFunctionArguments = false): array
+    public function getAllValues($element = null, bool $searchInFunctionArguments = false): array
     {
         $searchString = null;
         if ($element === null) {
@@ -70,7 +70,7 @@ public function getAllValues($element = null, $searchInFunctionArguments = false
      * @return array<int, Selector>
      * @example `getSelectorsBySpecificity('>= 100')`
      */
-    public function getSelectorsBySpecificity($specificitySearch = null): array
+    public function getSelectorsBySpecificity(?string $specificitySearch = null): array
     {
         /** @var array<int, Selector> $result */
         $result = [];