fix(curriculum): regex compatibility issue for Safari (#41725)

* fix(curriculum) regex compatibility issue for Safari

* fix: escape the dot parameter in regex

Co-authored-by: Oliver Eyton-Williams <ojeytonwilliams@gmail.com>
Co-authored-by: Tom <20648924+moT01@users.noreply.github.com>

curriculum/challenges/english/01-responsive-web-design/basic-css/change-a-variable-for-a-specific-area.md

@@ -23,10 +23,19 @@ The `penguin` class should reassign the `--penguin-belly` variable to `white`.
 
 ```js
 assert(
-  code.match(/\.penguin\s*?{[\s\S]*(?<!background-color: )--penguin-belly\s*?:\s?white\s*?;[\s\S]*}/gi)
+  code.match(/\.penguin\s*?{[\s\S]*--penguin-belly\s*?:\s*?white\s*?;[\s\S]*}/gi)
 );
 ```
 
+The `penguin` class should not contain the `background-color` property
+
+```js
+assert(
+  code.match(/^((?!background-color\s*?:\s*?)[\s\S])*$/g)
+);
+``` 
+
+
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