diff --git a/README.md b/README.md
index de4f1fb..f12f6b7 100644
--- a/README.md
+++ b/README.md
@@ -1,5 +1,7 @@
 # Collection of random CSS hacks for Firefox
 
+Stylesheets in this repository are tested only on Windows 10. They should work on current Nightlies but also generally on latest release Firefox unless otherwise noted.
+
 # Usage
 
 Use stylesheets under "chrome" in userChrome.css
@@ -10,4 +12,25 @@ You can import the stylesheets with @-rule import like this:
 
 ```css
 @import url("path/filename.css");
-```
\ No newline at end of file
+```
+
+## Important!
+
+Note that all `@import` rules need to be placed before any other rules in the file.
+
+# Theme
+
+Stylesheets prefixed with `theme_` require `theme_color_variables.css` to be imported.
+
+Example userChrome.css resulting in rather complete dark blueish-grey UI:
+
+```css
+@import url(theme_color_variables.css);
+@import url(theme_sidebar.css);
+@import url(theme_toolbars.css);
+@import url(theme_popups_and_menus.css);
+
+/* Your other rules here */
+```
+
+You can use individual modules from theme such as to only include popups_and_menus. But it would still be required that you import the theme_color_variables.css or you'll have to manually edit all the colors.