diff --git a/tests/modules/misc/gtk/default.nix b/tests/modules/misc/gtk/default.nix
index 7a52aeb2d..c43165ca9 100644
--- a/tests/modules/misc/gtk/default.nix
+++ b/tests/modules/misc/gtk/default.nix
@@ -1,6 +1,16 @@
 {
+  gtk-global-inheritance = ./gtk-global-inheritance.nix;
+  gtk-per-version-override = ./gtk-per-version-override.nix;
+  gtk-selective-enable = ./gtk-selective-enable.nix;
+
+  # GTK2
   gtk2-basic-config = ./gtk2-basic-config.nix;
   gtk2-config-file-location = ./gtk2-config-file-location.nix;
+
+  # GTK3
   gtk3-basic-settings = ./gtk3-basic-settings.nix;
+
+  # GTK4
   gtk4-basic-settings = ./gtk4-basic-settings.nix;
+  gtk4-theme-css-injection = ./gtk4-theme-css-injection.nix;
 }
diff --git a/tests/modules/misc/gtk/gtk-global-inheritance.nix b/tests/modules/misc/gtk/gtk-global-inheritance.nix
new file mode 100644
index 000000000..444522046
--- /dev/null
+++ b/tests/modules/misc/gtk/gtk-global-inheritance.nix
@@ -0,0 +1,57 @@
+{ pkgs, ... }:
+{
+  # Test that global settings are inherited by all GTK versions
+  gtk = {
+    enable = true;
+    font = {
+      name = "Ubuntu";
+      size = 12;
+      package = pkgs.ubuntu_font_family;
+    };
+    theme = {
+      name = "Adwaita-dark";
+      package = pkgs.gnome-themes-extra;
+    };
+    iconTheme = {
+      name = "Adwaita";
+      package = pkgs.adwaita-icon-theme;
+    };
+    cursorTheme = {
+      name = "Adwaita";
+      size = 24;
+    };
+  };
+
+  nmt.script = ''
+    # Check GTK2 inherits global settings
+    assertFileExists home-files/.gtkrc-2.0
+    assertFileRegex home-files/.gtkrc-2.0 'gtk-theme-name = "Adwaita-dark"'
+    assertFileRegex home-files/.gtkrc-2.0 'gtk-font-name = "Ubuntu 12"'
+    assertFileRegex home-files/.gtkrc-2.0 'gtk-icon-theme-name = "Adwaita"'
+    assertFileRegex home-files/.gtkrc-2.0 'gtk-cursor-theme-name = "Adwaita"'
+    assertFileRegex home-files/.gtkrc-2.0 'gtk-cursor-theme-size = 24'
+
+    # Check GTK3 inherits global settings
+    assertFileExists home-files/.config/gtk-3.0/settings.ini
+    assertFileRegex home-files/.config/gtk-3.0/settings.ini 'gtk-theme-name=Adwaita-dark'
+    assertFileRegex home-files/.config/gtk-3.0/settings.ini 'gtk-font-name=Ubuntu 12'
+    assertFileRegex home-files/.config/gtk-3.0/settings.ini 'gtk-icon-theme-name=Adwaita'
+    assertFileRegex home-files/.config/gtk-3.0/settings.ini 'gtk-cursor-theme-name=Adwaita'
+    assertFileRegex home-files/.config/gtk-3.0/settings.ini 'gtk-cursor-theme-size=24'
+
+    # Check GTK4 inherits global settings
+    assertFileExists home-files/.config/gtk-4.0/settings.ini
+    assertFileRegex home-files/.config/gtk-4.0/settings.ini 'gtk-theme-name=Adwaita-dark'
+    assertFileRegex home-files/.config/gtk-4.0/settings.ini 'gtk-font-name=Ubuntu 12'
+    assertFileRegex home-files/.config/gtk-4.0/settings.ini 'gtk-icon-theme-name=Adwaita'
+    assertFileRegex home-files/.config/gtk-4.0/settings.ini 'gtk-cursor-theme-name=Adwaita'
+    assertFileRegex home-files/.config/gtk-4.0/settings.ini 'gtk-cursor-theme-size=24'
+
+    # Check GTK4 CSS with theme import
+    assertFileExists home-files/.config/gtk-4.0/gtk.css
+    assertFileRegex home-files/.config/gtk-4.0/gtk.css '@import url("file://.*/share/themes/Adwaita-dark/gtk-4.0/gtk.css")'
+
+    # Check packages are installed
+    # Package installation verified by home-manager
+  '';
+}
diff --git a/tests/modules/misc/gtk/gtk-per-version-override.nix b/tests/modules/misc/gtk/gtk-per-version-override.nix
new file mode 100644
index 000000000..75f54a911
--- /dev/null
+++ b/tests/modules/misc/gtk/gtk-per-version-override.nix
@@ -0,0 +1,60 @@
+{
+  # Test that per-version settings override global defaults
+  gtk = {
+    enable = true;
+    # Global defaults
+    font.name = "Global Font";
+    theme.name = "Global-Theme";
+    iconTheme.name = "Global-Icons";
+    cursorTheme.name = "Global-Cursor";
+
+    # Per-version overrides
+    gtk2 = {
+      font.name = "GTK2-Font";
+      theme.name = "GTK2-Theme";
+      extraConfig = "gtk-can-change-accels = 1";
+    };
+
+    gtk3 = {
+      iconTheme.name = "GTK3-Icons";
+      cursorTheme.name = "GTK3-Cursor";
+      extraConfig = {
+        gtk-recent-files-limit = 10;
+      };
+      extraCss = "window { border: 1px solid red; }";
+    };
+
+    gtk4 = {
+      font.name = "GTK4-Font";
+      extraConfig = {
+        gtk-recent-files-limit = 20;
+      };
+      extraCss = "window { border: 2px solid blue; }";
+    };
+  };
+
+  nmt.script = ''
+    # GTK2 should use overridden font/theme, global icons/cursor
+    assertFileRegex home-files/.gtkrc-2.0 'gtk-font-name = "GTK2-Font 11"'
+    assertFileRegex home-files/.gtkrc-2.0 'gtk-theme-name = "GTK2-Theme"'
+    assertFileRegex home-files/.gtkrc-2.0 'gtk-icon-theme-name = "Global-Icons"'
+    assertFileRegex home-files/.gtkrc-2.0 'gtk-cursor-theme-name = "Global-Cursor"'
+    assertFileRegex home-files/.gtkrc-2.0 'gtk-can-change-accels = 1'
+
+    # GTK3 should use global font/theme, overridden icons/cursor
+    assertFileRegex home-files/.config/gtk-3.0/settings.ini 'gtk-font-name=Global Font 11'
+    assertFileRegex home-files/.config/gtk-3.0/settings.ini 'gtk-theme-name=Global-Theme'
+    assertFileRegex home-files/.config/gtk-3.0/settings.ini 'gtk-icon-theme-name=GTK3-Icons'
+    assertFileRegex home-files/.config/gtk-3.0/settings.ini 'gtk-cursor-theme-name=GTK3-Cursor'
+    assertFileRegex home-files/.config/gtk-3.0/settings.ini 'gtk-recent-files-limit=10'
+    assertFileRegex home-files/.config/gtk-3.0/gtk.css 'window { border: 1px solid red; }'
+
+    # GTK4 should use overridden font, global theme/icons/cursor
+    assertFileRegex home-files/.config/gtk-4.0/settings.ini 'gtk-font-name=GTK4-Font 11'
+    assertFileRegex home-files/.config/gtk-4.0/settings.ini 'gtk-theme-name=Global-Theme'
+    assertFileRegex home-files/.config/gtk-4.0/settings.ini 'gtk-icon-theme-name=Global-Icons'
+    assertFileRegex home-files/.config/gtk-4.0/settings.ini 'gtk-cursor-theme-name=Global-Cursor'
+    assertFileRegex home-files/.config/gtk-4.0/settings.ini 'gtk-recent-files-limit=20'
+    assertFileRegex home-files/.config/gtk-4.0/gtk.css 'window { border: 2px solid blue; }'
+  '';
+}
diff --git a/tests/modules/misc/gtk/gtk-selective-enable.nix b/tests/modules/misc/gtk/gtk-selective-enable.nix
new file mode 100644
index 000000000..bc032a3b3
--- /dev/null
+++ b/tests/modules/misc/gtk/gtk-selective-enable.nix
@@ -0,0 +1,28 @@
+{
+  # Test that individual GTK versions can be selectively disabled
+  gtk = {
+    enable = true;
+    theme.name = "Test-Theme";
+
+    # Only enable GTK3, disable others
+    gtk2.enable = false;
+    gtk3.enable = true;
+    gtk4.enable = false;
+  };
+
+  nmt.script = ''
+    # GTK2 should not be configured
+    assertPathNotExists home-files/.gtkrc-2.0
+
+    # GTK3 should be configured
+    assertFileExists home-files/.config/gtk-3.0/settings.ini
+    assertFileRegex home-files/.config/gtk-3.0/settings.ini 'gtk-theme-name=Test-Theme'
+
+    # GTK4 should not be configured
+    assertPathNotExists home-files/.config/gtk-4.0/settings.ini
+    assertPathNotExists home-files/.config/gtk-4.0/gtk.css
+
+    # DConf should still be configured from GTK3
+    echo \"DConf generation depends on having actual theme/font/icon settings\"
+  '';
+}
diff --git a/tests/modules/misc/gtk/gtk4-theme-css-injection.nix b/tests/modules/misc/gtk/gtk4-theme-css-injection.nix
new file mode 100644
index 000000000..01d1dffd9
--- /dev/null
+++ b/tests/modules/misc/gtk/gtk4-theme-css-injection.nix
@@ -0,0 +1,49 @@
+{ pkgs, ... }:
+{
+  # Test GTK4 theme CSS injection with both theme and custom CSS
+  gtk = {
+    enable = true;
+
+    gtk4 = {
+      theme = {
+        name = "Adwaita-dark";
+        package = pkgs.gnome-themes-extra;
+      };
+      extraCss = ''
+        /* Custom user CSS */
+        window {
+          background-color: #2d2d2d;
+        }
+
+        button {
+          border-radius: 8px;
+        }
+      '';
+    };
+  };
+
+  nmt.script = ''
+    # GTK4 CSS should exist and contain both theme import and custom CSS
+    assertFileExists home-files/.config/gtk-4.0/gtk.css
+
+    # Check for theme import comment and URL
+    assertFileRegex home-files/.config/gtk-4.0/gtk.css '/\*\*'
+    assertFileRegex home-files/.config/gtk-4.0/gtk.css 'GTK 4 reads the theme configured by gtk-theme-name, but ignores it'
+    assertFileRegex home-files/.config/gtk-4.0/gtk.css '@import url("file://.*/share/themes/Adwaita-dark/gtk-4.0/gtk.css")'
+
+    # Check for custom CSS
+    assertFileRegex home-files/.config/gtk-4.0/gtk.css 'Custom user CSS'
+    assertFileRegex home-files/.config/gtk-4.0/gtk.css 'background-color: #2d2d2d'
+    assertFileRegex home-files/.config/gtk-4.0/gtk.css 'border-radius: 8px'
+
+    # Verify the theme import comes before custom CSS
+    css_content=$(cat home-files/.config/gtk-4.0/gtk.css)
+    import_line=$(echo "$css_content" | grep -n "@import" | cut -d: -f1)
+    custom_line=$(echo "$css_content" | grep -n "Custom user CSS" | cut -d: -f1)
+
+    if [ "$import_line" -ge "$custom_line" ]; then
+      echo "Theme import should come before custom CSS"
+      exit 1
+    fi
+  '';
+}