feature: snacks.picker support

[theol0403]

New picker is awesome: https://github.com/folke/snacks.nvim/blob/main/docs/picker.md

But, it is broken with this theme:

Fzf, by contrast, is beautiful.

If no one wants to tackle this, I'll take a look one day when I have a chance and make a PR.

[narutozxp]

override  = function(c) 
    return {
    ["NonText"] = {fg = "#545c7e"},
}
end,

[theol0403]

Needs to be more than that, primarily in the background and border lines. That nontext color also does not seem like a real theme color