diff --git a/modules/regreet/gtk.css.mustache b/modules/regreet/gtk.css.mustache
new file mode 100644
index 00000000..3b2e9224
--- /dev/null
+++ b/modules/regreet/gtk.css.mustache
@@ -0,0 +1,88 @@
+@define-color accent_color #{{base0D-hex}};
+@define-color accent_bg_color #{{base0D-hex}};
+@define-color accent_fg_color #{{base00-hex}};
+@define-color destructive_color #{{base08-hex}};
+@define-color destructive_bg_color #{{base08-hex}};
+@define-color destructive_fg_color #{{base00-hex}};
+@define-color success_color #{{base0B-hex}};
+@define-color success_bg_color #{{base0B-hex}};
+@define-color success_fg_color #{{base00-hex}};
+@define-color warning_color #{{base0E-hex}};
+@define-color warning_bg_color #{{base0E-hex}};
+@define-color warning_fg_color #{{base00-hex}};
+@define-color error_color #{{base08-hex}};
+@define-color error_bg_color #{{base08-hex}};
+@define-color error_fg_color #{{base00-hex}};
+@define-color window_bg_color #{{base00-hex}};
+@define-color window_fg_color #{{base05-hex}};
+@define-color view_bg_color #{{base00-hex}};
+@define-color view_fg_color #{{base05-hex}};
+@define-color headerbar_bg_color #{{base01-hex}};
+@define-color headerbar_fg_color #{{base05-hex}};
+@define-color headerbar_border_color rgba({{base01-dec-r}}, {{base01-dec-g}}, {{base01-dec-b}}, 0.7);
+@define-color headerbar_backdrop_color @window_bg_color;
+@define-color headerbar_shade_color rgba(0, 0, 0, 0.07);
+@define-color headerbar_darker_shade_color rgba(0, 0, 0, 0.07);
+@define-color sidebar_bg_color #{{base01-hex}};
+@define-color sidebar_fg_color #{{base05-hex}};
+@define-color sidebar_backdrop_color @window_bg_color;
+@define-color sidebar_shade_color rgba(0, 0, 0, 0.07);
+@define-color secondary_sidebar_bg_color @sidebar_bg_color;
+@define-color secondary_sidebar_fg_color @sidebar_fg_color;
+@define-color secondary_sidebar_backdrop_color @sidebar_backdrop_color;
+@define-color secondary_sidebar_shade_color @sidebar_shade_color;
+@define-color card_bg_color #{{base01-hex}};
+@define-color card_fg_color #{{base05-hex}};
+@define-color card_shade_color rgba(0, 0, 0, 0.07);
+@define-color dialog_bg_color #{{base01-hex}};
+@define-color dialog_fg_color #{{base05-hex}};
+@define-color popover_bg_color #{{base01-hex}};
+@define-color popover_fg_color #{{base05-hex}};
+@define-color popover_shade_color rgba(0, 0, 0, 0.07);
+@define-color shade_color rgba(0, 0, 0, 0.07);
+@define-color scrollbar_outline_color #{{base02-hex}};
+@define-color blue_1 #{{base0D-hex}};
+@define-color blue_2 #{{base0D-hex}};
+@define-color blue_3 #{{base0D-hex}};
+@define-color blue_4 #{{base0D-hex}};
+@define-color blue_5 #{{base0D-hex}};
+@define-color green_1 #{{base0B-hex}};
+@define-color green_2 #{{base0B-hex}};
+@define-color green_3 #{{base0B-hex}};
+@define-color green_4 #{{base0B-hex}};
+@define-color green_5 #{{base0B-hex}};
+@define-color yellow_1 #{{base0A-hex}};
+@define-color yellow_2 #{{base0A-hex}};
+@define-color yellow_3 #{{base0A-hex}};
+@define-color yellow_4 #{{base0A-hex}};
+@define-color yellow_5 #{{base0A-hex}};
+@define-color orange_1 #{{base09-hex}};
+@define-color orange_2 #{{base09-hex}};
+@define-color orange_3 #{{base09-hex}};
+@define-color orange_4 #{{base09-hex}};
+@define-color orange_5 #{{base09-hex}};
+@define-color red_1 #{{base08-hex}};
+@define-color red_2 #{{base08-hex}};
+@define-color red_3 #{{base08-hex}};
+@define-color red_4 #{{base08-hex}};
+@define-color red_5 #{{base08-hex}};
+@define-color purple_1 #{{base0E-hex}};
+@define-color purple_2 #{{base0E-hex}};
+@define-color purple_3 #{{base0E-hex}};
+@define-color purple_4 #{{base0E-hex}};
+@define-color purple_5 #{{base0E-hex}};
+@define-color brown_1 #{{base0F-hex}};
+@define-color brown_2 #{{base0F-hex}};
+@define-color brown_3 #{{base0F-hex}};
+@define-color brown_4 #{{base0F-hex}};
+@define-color brown_5 #{{base0F-hex}};
+@define-color light_1 #{{base05-hex}};
+@define-color light_2 #{{base05-hex}};
+@define-color light_3 #{{base05-hex}};
+@define-color light_4 #{{base05-hex}};
+@define-color light_5 #{{base05-hex}};
+@define-color dark_1 #{{base05-hex}};
+@define-color dark_2 #{{base05-hex}};
+@define-color dark_3 #{{base05-hex}};
+@define-color dark_4 #{{base05-hex}};
+@define-color dark_5 #{{base05-hex}};
diff --git a/modules/regreet/nixos.nix b/modules/regreet/nixos.nix
index fc85a757..54ba913a 100644
--- a/modules/regreet/nixos.nix
+++ b/modules/regreet/nixos.nix
@@ -12,7 +12,17 @@ mkTarget {
   autoEnable = pkgs.stdenv.hostPlatform.isLinux;
   autoEnableExpr = "pkgs.stdenv.hostPlatform.isLinux";
 
-  extraOptions.useWallpaper = config.lib.stylix.mkEnableWallpaper "ReGreet" true;
+  extraOptions = {
+    useWallpaper = config.lib.stylix.mkEnableWallpaper "ReGreet" true;
+    extraCss = lib.mkOption {
+      description = ''
+        Extra code added to `programs.regreet.extraCss` option.
+      '';
+      type = lib.types.lines;
+      default = "";
+      example = "window.background { border-radius: 0; }";
+    };
+  };
 
   configElements = [
     {
@@ -34,6 +44,24 @@ mkTarget {
         name = "adw-gtk3";
       };
     }
+    (
+      { cfg, colors }:
+      let
+        baseCss = colors {
+          # This is strongly inspired by ../gtk/gtk.mustache.
+          template = ./gtk.css.mustache;
+          extension = ".css";
+        };
+
+        finalCss = pkgs.runCommandLocal "gtk.css" { } ''
+          cat ${baseCss} >>$out
+          echo ${lib.escapeShellArg cfg.extraCss} >>$out
+        '';
+      in
+      {
+        programs.regreet.extraCss = finalCss.outPath;
+      }
+    )
     (
       { polarity }:
       {
@@ -79,5 +107,14 @@ mkTarget {
         };
       }
     )
+    (
+      { polarity, icons }:
+      {
+        programs.regreet.iconTheme = {
+          inherit (icons) package;
+          name = if (polarity == "dark") then icons.dark else icons.light;
+        };
+      }
+    )
   ];
 }
diff --git a/modules/regreet/testbeds/regreet.nix b/modules/regreet/testbeds/regreet.nix
new file mode 100644
index 00000000..a4ec92ae
--- /dev/null
+++ b/modules/regreet/testbeds/regreet.nix
@@ -0,0 +1 @@
+{ programs.regreet.enable = true; }