Set input font size to be 16px on mobile

For some dumb reason, any inputs with a smaller font size than `16px`
will cause the browser on mobile (I think only Safari) to "zoom" in on
the field. On the event registration modal, this causes annoying bugs
when trying to search for attendees.

app/styles/globals.css

@@ -110,6 +110,12 @@ th:last-child {
   border-radius: 0 2em 2em 0;
 }
 
+input {
+  @media (--mobile-device) {
+    font-size: var(--font-size-md);
+  }
+}
+
 label {
   display: block;
 }