refactor: use the sr-only class to visually hide element (#51931)

client/src/templates/Challenges/exam/exam.css

@@ -55,11 +55,6 @@
   margin: 0;
 }
 
-.exam-answer-input-hidden {
-  position: absolute;
-  left: -9999px;
-}
-
 .exam-answer-input-visible {
   margin-inline-end: 15px;
   position: relative;

client/src/templates/Challenges/exam/show.tsx

@@ -423,7 +423,7 @@ class ShowExam extends Component<ShowExamProps, ShowExamState> {
                               userExamQuestions[currentQuestionIndex].answer
                                 .id === id
                             }
-                            className='exam-answer-input-hidden'
+                            className='sr-only'
                             name={id}
                             onChange={() =>
                               this.selectAnswer(