feat: show active player

src/Calendar.tsx

@@ -89,7 +89,7 @@ const Calendar = ({ playerId }: { playerId: number }) => {
       const date = new Date(0);
       date.setDate(i + 5);
       days.push(
-        <div key={"weekday_" + i} className="empty">
+        <div key={"weekday_" + i} className="weekday">
           {date.toLocaleString("default", {
             weekday: "short",
           })}
@@ -111,7 +111,12 @@ const Calendar = ({ playerId }: { playerId: number }) => {
       days.push(
         <div
           key={date.getDate()}
-          className="day"
+          className={
+            "day" +
+            (date.toDateString() === selectedDate.toDateString()
+              ? " selected-day"
+              : "")
+          }
           onClick={() => handleDayClick(date)}
         >
           <div