diff --git a/res/css/_sc/README.md b/res/css/_sc/README.md
index 8491c8956c9..6c81993124e 100644
--- a/res/css/_sc/README.md
+++ b/res/css/_sc/README.md
@@ -24,4 +24,4 @@ Even if the properties are styled with `!important` by the upstream to cover reg
 
 The way in which the upstream project generates concatenated CSS files has been very stable (essentially same since at least 2018. See: https://github.com/matrix-org/matrix-react-sdk/commits/develop/res/css/rethemendex.sh), so we should be able to depend on the current way how it works for a reasonable time.
 
-**Warning: running `rethemendex` breaks cascading!** Manual editing is required for now.
+**Please do not forget to update `_customization.pcss`** if you have added other CSS files for customization. Please mind where to import the files as it affects how styles cascade. Never import them alphabetically.
diff --git a/res/css/_sc/_customization.pcss b/res/css/_sc/_customization.pcss
index 9806176c51b..4ac7dc0644c 100644
--- a/res/css/_sc/_customization.pcss
+++ b/res/css/_sc/_customization.pcss
@@ -15,5 +15,7 @@ limitations under the License.
 */
 
 /* TODO: replace @import with @mixin once multiple CSS files are created for customization in order to keep styling modular */
+/* Please mind where to import CSS files as it affects how styles cascade. */
+
 @import "./views/rooms/_EventTile.pcss";
 @import "./views/rooms/_IRClayout.pcss";
diff --git a/res/css/rethemendex.sh b/res/css/rethemendex.sh
index 37090b96d8f..1bfcaa521d2 100755
--- a/res/css/rethemendex.sh
+++ b/res/css/rethemendex.sh
@@ -8,8 +8,17 @@ cd `dirname $0`
     # we used to have exclude /themes from the find at this point.
     # as themes are no longer a spurious subdirectory of css/, we don't
     # need it any more.
-    find . -iname _\*.pcss | fgrep -v _components.pcss | LC_ALL=C sort |
+    #
+    # Exclude "_sc" folder dedicated for our custom CSS files from being included
+    # to alphabetic sorting which causes cascading mess. Please note that CSS files
+    # inside the folder are imported at the end.
+    find . -iname _\*.pcss -not -path "./_sc/*" | fgrep -v _components.pcss | LC_ALL=C sort |
         while read i; do
             echo "@import \"$i\";"
         done
+
+        # Import the CSS file dedicated for customization to let our declarations
+        # inside it override the styles specified by the upstream project.
+        echo "\n/* Customization for SchildiChat */";
+        echo "@import \"./_sc/_customization.pcss\";";
 } > _components.pcss