add dist file to customize css

screen_custom.css.dist

+/**
+    Copy the dist file to "screen_custom.css" to enable it
+    Then you can override styles of all css
+
+    Example: 
+    Plain white background and remove border of the main box
+*/
+:root{
+    --main-bg: #fff;
+    --content-border: none;
+}
\ No newline at end of file