replace the word "dashes" with "hyphens" (#37705)

curriculum/challenges/english/01-responsive-web-design/basic-css/create-a-custom-css-variable.english.md

@@ -8,7 +8,7 @@ forumTopicId: 301086
 
 ## Description
 <section id='description'>
-To create a CSS variable, you just need to give it a name with two dashes in front of it and assign it a value like this:
+To create a CSS variable, you just need to give it a name with two hyphens in front of it and assign it a value like this:
 
 ```css
 --penguin-skin: gray;