Fixed custom colors example in documentation

Author: squidfunk

docs/setup/changing-the-colors.md

@@ -283,7 +283,7 @@ add:
 === ":octicons-file-code-16: docs/stylesheets/extra.css"
 
     ``` css
-    :root {
+    :root > * {
       --md-primary-fg-color:        #EE0F0F;
       --md-primary-fg-color--light: #ECB7B7;
       --md-primary-fg-color--dark:  #90030C;