fix text editor 取消上标下标

src/features/OnlineExam/Examing/TextQuestionView.vue

@@ -351,7 +351,8 @@ export default {
       }
     },
     undoTextSup() {
-      // getSelection().modify("extend", "left", "character");
+      // 取消上标时，必须选择之前的文字，才能实现
+      getSelection().modify("extend", "left", "character");
       let selRange = getSelection().getRangeAt(0);
       var documentFragment = selRange.extractContents();
       var text = new Text(documentFragment.textContent);
@@ -451,6 +452,7 @@ export default {
   max-width: 500px;
   min-height: 300px;
   border: 1px solid grey;
+  padding: 2px;
 }
 
 .audio-answer {