Allow changing z-index in custom theming

[arcoraven]

Problem
The RainbowKit modal sets a z-index of 2147483646.

Use case
I'm building a custom connector that pops up a modal with the exact same z-index, but RainbowKit shows up on top because it's later in the DOM.

Proposed solution
Allow setting a zIndex prop in a custom theme so I can lower it as needed.

Right now this is my workaround:

[data-rk] [aria-labelledby="rk_connect_title"] {
  z-index: 2147483645 !important;
}

[mentasuave01]

thanks mate, I'm stealing this