fix: set tabIndex to 0 when day is focused

packages/react-day-picker/src/hooks/useDayRender/useDayRender.test.tsx

@@ -296,6 +296,20 @@ describe('when the day is target of focus but outside', () => {
   });
 });
 
+describe('when the day is focused', () => {
+  const date = today;
+  const focusContext: FocusContextValue = {
+    ...mockedFocusContext,
+    focusedDay: date
+  };
+  beforeEach(() => {
+    setup(date, date, {}, { focus: focusContext });
+  });
+  test('the button should have tabIndex 0', () => {
+    expect(result.current.buttonProps.tabIndex).toBe(0);
+  });
+});
+
 describe('when the day is disabled', () => {
   const date = today;
   const dayPickerProps = {

packages/react-day-picker/src/hooks/useDayRender/useDayRender.tsx

@@ -104,12 +104,15 @@ export function useDayRender(
     isSameDay(focusContext.focusTarget, day) &&
     !activeModifiers.outside;
 
+  const isFocused =
+    focusContext.focusedDay && isSameDay(focusContext.focusedDay, day);
+
   const buttonProps = {
     ...divProps,
     disabled: activeModifiers.disabled,
     ['aria-pressed']: activeModifiers.selected,
     ['aria-label']: ariaLabel,
-    tabIndex: isFocusTarget ? 0 : -1,
+    tabIndex: isFocused || isFocusTarget ? 0 : -1,
     ...eventHandlers
   };