fix(curriculum): typo in css backgrounds and borders quiz (freeCodeCamp#59220)

Author: Supravisor

curriculum/challenges/english/25-front-end-development/quiz-css-backgrounds-and-borders/66ed8fd7f45ce3ece4053eb0.md

@@ -407,7 +407,7 @@ Which of these is NOT a valid `border` value?
 
 #### --text--
 
-What is does the `radial-gradient` function do?
+What does the `radial-gradient` function do?
 
 #### --distractors--