do not bail out if start and end are unordered

components/wizard/calendar.tsx

@@ -23,6 +23,22 @@ export default function MyCalendar() {
   const prevBooked = inSelection && getNextSmaller(daysBooked, start)
   const nextBooked = inSelection && getNextBigger(daysBooked, start)
 
+  function isSelected(date: Date) {
+    if (!startDate) {
+      return false
+    }
+
+    // if end is before start, it is not within
+    if (endDate && !isAfter(endDate, startDate)) {
+      return false
+    }
+
+    return isWithinInterval(date, {
+      start: startDate,
+      end: endDate || startDate,
+    })
+  }
+
   function tileClassName({ date, view }) {
     const isMonthView = view === 'month'
     const isDaysBookedLoaded = !!daysBooked
@@ -37,12 +53,7 @@ export default function MyCalendar() {
       'react-calendar__tile--selected-start': isSameDay(date, startDate),
       'react-calendar__tile--selected-end': isSameDay(date, endDate),
       'react-calendar__tile--selected':
-        (startDate &&
-          isWithinInterval(date, {
-            start: startDate,
-            end: endDate || startDate,
-          })) ||
-        isSameDay(date, startDate),
+        isSelected(date) || isSameDay(date, startDate),
       'react-calendar__tile--unselectable':
         inSelection &&
         ((prevBooked && date < new Date(prevBooked)) ||