fix: wrong text-color class and text contrast on dates page (#1223)

src/course-home/dates-tab/timeline/badgelist.jsx

@@ -38,21 +38,21 @@ function getBadgeListAndColor(date, intl, item, items) {
       message: messages.today,
       shownForDay: isToday,
       bg: 'bg-warning-300',
-      className: 'text-black',
+      className: 'text-dark',
     },
     {
       message: messages.completed,
       shownForDay: assignments.length && assignments.every(isComplete),
       shownForItem: x => isLearnerAssignment(x) && isComplete(x),
       bg: 'bg-light-500',
-      className: 'text-black',
+      className: 'text-dark',
     },
     {
       message: messages.pastDue,
       shownForDay: assignments.length && assignments.every(isPastDue),
       shownForItem: x => isLearnerAssignment(x) && isPastDue(x),
       bg: 'bg-dark-200',
-      className: 'text-white',
+      className: 'text-dark',
     },
     {
       message: messages.dueNext,