Okay, for anyone who has the same issue with a Gantry 4 tempate (hopefully I'll be losing the Gantry templates soon), here is the answer. Also, dear Fabrik people, troester, and everyone who has always helped out: I would pay for support like I used to, but the company has said it's too difficult to invoice.
I added the following to my custom css file after noticing I'd already added some to the Gantry template css to get the csv download modal working. This is a great feeling for 4:43 p.m. on my last day in the office before a vacation during a pandemic! Yay, a small victory.
div.modal {
position: fixed;
top: 5%;
left: 50%;
z-index: 1050;
width: 80%;
margin-left: -40%;
background-color: #fff;
border: 1px solid #999;
border: 1px solid rgba(0,0,0,0.3);
*border: 1px solid #999;
-webkit-border-radius: 6px;
-moz-border-radius: 6px;
border-radius: 6px;
-webkit-box-shadow: 0 3px 7px rgba(0,0,0,0.3);
-moz-box-shadow: 0 3px 7px rgba(0,0,0,0.3);
box-shadow: 0 3px 7px rgba(0,0,0,0.3);
-webkit-background-clip: padding-box;
-moz-background-clip: padding-box;
background-clip: padding-box;
outline: none;
}
div.modal.fade {
-webkit-transition: opacity .3s linear, top .3s ease-out;
-moz-transition: opacity .3s linear, top .3s ease-out;
-o-transition: opacity .3s linear, top .3s ease-out;
transition: opacity .3s linear, top .3s ease-out;
top: -25%;
}