Accessibility issue with shortcut panel close button

[Maksim-Skvortsov]

react-dates version
e.g. react-dates@18.3.1

Describe the bug
When focus on input and we open shortcut panel through shift + ? shortcut there's no focus on the close button so we can't close it by hitting enter

Steps to reproduce the behavior

• Click on the either input to open calendar
• Press shift + ? shortcut to open shortcut panel
• Note that there's no focus on the close button so we can't close that by hitting enter

Screenshots/Gifs

Is the issue reproducible in Storybook?
Yes, for example https://react-dates.github.io/react-dates/?path=/story/daterangepicker-drp--default