Style common dialog popup

alternative_user_files/userChrome_windows.css

@@ -161,6 +161,13 @@ listitem[selected="true"] {
   border: 1px solid var(--grey-50) !important;
   box-shadow: none !important;
 }
+@-moz-document url("chrome://global/content/commonDialog.xul")  {
+  #commonDialog {
+    -moz-appearance: none !important;
+    background: var(--primary-dark-color) !important;
+    color: var(--primary-light-color) !important;
+  }
+}
 /* The following code is based on that found on
 * https://www.jeffersonscher.com/gm/url-bar-tweaks.html
 * Copyright © 2017 Jefferson Scher (BSD-3-Clause License or CC-BY License) */

userChrome-files/common_dialog.css

@@ -0,0 +1,7 @@
+@-moz-document url("chrome://global/content/commonDialog.xul"){
+  #commonDialog{
+    -moz-appearance: none !important;
+    background: var(--primary-dark-color) !important;
+    color: var(--primary-light-color) !important;
+  }
+}

userChrome.css

@@ -161,6 +161,13 @@ listitem[selected="true"] {
   border: 1px solid var(--grey-50) !important;
   box-shadow: none !important;
 }
+@-moz-document url("chrome://global/content/commonDialog.xul")  {
+  #commonDialog {
+    -moz-appearance: none !important;
+    background: var(--primary-dark-color) !important;
+    color: var(--primary-light-color) !important;
+  }
+}
 /* The following code is based on that found on
 * https://www.jeffersonscher.com/gm/url-bar-tweaks.html
 * Copyright © 2017 Jefferson Scher (BSD-3-Clause License or CC-BY License) */

userChrome_imports.css

@@ -14,3 +14,4 @@
 @import "userChrome-files/page_info.css";
 @import "userChrome-files/findbar.css";
 @import "userChrome-files/bookmarks_popup.css";
+@import "userChrome-files/common_dialog.css";