I have a client who has been using the All-In-One Calendar by Timely for 6-8 months now. After a recent upgrade to the newest WordPress, the Calendar has dropped it's style and is now picking up the theme's stylesheet.
This isn't a huge deal, except it is affecting all the calendar menus and dropdowns for view options and Filters.
Here is the current calendar page: http://www.isd47.org/calendar-news/district-calendar/all-district-calendar/
And here is a screencap of what it looked like previously: