Good evening Amanda and welcome back!
Thank you for reaching out to us.
We are sorry to hear about the Events in sliding under your header.
I would love to help you with this topic.
The simplest solution would be to simply increase the z-index value of the date picker.
Try adding the following CSS rule to your style.css file or in your Custom CSS metabox:
.datepicker.dropdown-menu {z-index: 9999 !important}
This will bring the date picker over your menu (which I understand is not your preferred option).
You could always force a different position for the date picker instead, but to do that you will be fighting with real-time generated “top” position values (that are designed to make the filter responsive. In other words you will need to adjust the value for different screen widths (using @media CSS queries).
Here is an idea of what that might look like
.datepicker.dropdown-menu {top: 380px !important}
Let me know if that helps.
Have a great day!
Geoff B.