Thanks for your quick reply and help.
I got it to work by using this single line of custom CSS.
.stk-f59b0b1 {z-index: 2;}
I assumed that this would only work for a single page. It ended up working for all the elements on the pages that I have tested so far, except one, an input text box in the middle of a form (https://www.staging2.everygoodgift.org/contact-us/). To see it, scroll down the page until it appears with the slide out menu up.
I don’t really understand why that single CSS line should work across the website. Could you explain it better to me? I understand z-order. I don’t understand why changing a single element on one page had such an “almost universal” effect.
The truth is, I would prefer not to think that I have to go find all the elements on all the pages that somehow bleed through.
I tried setting z-index to 9999 on the slide out menu background, thinking that might do it. Is that a possibility? If so, what is the CSS?