Main Page Dropdown Menu on Mobile *hides behind* image slider

It was brought to my attention that the top navigation menu drops down behind the slider on the main page when viewing on mobile or when viewing on PC if the browser window is half-sized.

Repeatable issue:
-Checked with both iOS and Android.
-Checked with Safari and Chrome on iOS, just Chrome on Android.
-Checked with PC using Chrome, half-width screen.

Have you encountered this issue before? Is there a known fix?

-Marjorie