overwrite gruvbox theme

modules/nvim.nix

@@ -79,7 +79,18 @@
         enable = true;
         settings = {
           options = {
-            theme = "gruvbox_dark";
+            theme.__raw = ''
+              (function()
+                local theme = require('lualine.themes.gruvbox_dark')
+                for _, mode in ipairs({'insert', 'visual', 'replace', 'command'}) do
+                  if theme[mode] then
+                    theme[mode].b = theme.normal.b
+                    theme[mode].c = theme.normal.c
+                  end
+                end
+                return theme
+              end)()
+            '';
             component_separators = { left = "|"; right = "|"; };
             section_separators = { left = " "; right = " "; };
           };