fix: button hover background color (#1653)

This PR updates the hover background for the top navigation buttons that are shown when the left side navigation is enabled. The hover background is updated to match the hover background of other existing IconButton components, see DiscussionNotificationTrigger.jsx, on the page.

Author: KristinAoki

src/courseware/course/sequence/sequence-navigation/generic/NextButton.jsx

@@ -47,8 +47,7 @@ const NextButton = ({
   if (isAtTop) {
     return (
       <IconButton
-        variant="light"
-        className={buttonStyle}
+        className={`${buttonStyle} icon-hover`}
         onClick={onClick}
         src={nextArrow}
         disabled={disabled}

src/courseware/course/sequence/sequence-navigation/generic/PreviousButton.jsx

@@ -40,8 +40,7 @@ const PreviousButton = ({
   if (isAtTop) {
     return (
       <IconButton
-        variant="light"
-        className={buttonStyle}
+        className={`${buttonStyle} icon-hover`}
         onClick={onClickHandler}
         src={prevArrow}
         disabled={disabled}