Transparency with winblend

[axieax]

Hi, it would be nice to be able to set transparency of the popup window using vim.api.nvim_win_set_option(winnr, "winblend", ?), where ? can be passed in as a config option :))

[axieax]

Just realised that you use nui.nvim for popups, so here's a PR to add support for customising its options. Example config for transparency:

require("regexplainer".setup({
  popup = {
    win_options = {
      winblend = 20,
    },
  },
})