diff --git a/res/css/_components.pcss b/res/css/_components.pcss
index 12d2457fc5d1..8ddcf474cf87 100644
--- a/res/css/_components.pcss
+++ b/res/css/_components.pcss
@@ -382,3 +382,6 @@
 @import "./voice-broadcast/atoms/_VoiceBroadcastRecordingConnectionError.pcss";
 @import "./voice-broadcast/atoms/_VoiceBroadcastRoomSubtitle.pcss";
 @import "./voice-broadcast/molecules/_VoiceBroadcastBody.pcss";
+
+/* Customization for SchildiChat */
+@import "./_sc/_customization.pcss";
diff --git a/res/css/_sc/README.md b/res/css/_sc/README.md
new file mode 100644
index 000000000000..2305a6787eff
--- /dev/null
+++ b/res/css/_sc/README.md
@@ -0,0 +1,21 @@
+<!--
+Copyright 2024 Suguru Hirahara
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+-->
+
+# `_sc` folder for customization
+
+For customization, import a custom CSS file on `res/css/_sc/_customization.pcss` and put anything such as custom CSS declarations and variables in it to let them override the values inherited from the upstream.
+
+Please mind where to import a new CSS file. **Never sort the files alphabetically as it breaks how styles cascade.**
diff --git a/res/css/_sc/_customization.pcss b/res/css/_sc/_customization.pcss
new file mode 100644
index 000000000000..31ef3e71b5da
--- /dev/null
+++ b/res/css/_sc/_customization.pcss
@@ -0,0 +1,19 @@
+/*
+Copyright 2024 Suguru Hirahara
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+/* TODO: use @mixin or something for scoping once multiple CSS files are created
+   for customization in order to keep styling modular */
+/* Please mind where to import CSS files as it might affect how styles cascade. */
diff --git a/res/css/rethemendex.sh b/res/css/rethemendex.sh
index 37090b96d8fb..db4b0db8c30c 100755
--- a/res/css/rethemendex.sh
+++ b/res/css/rethemendex.sh
@@ -8,8 +8,18 @@ cd `dirname $0`
     # we used to have exclude /themes from the find at this point.
     # as themes are no longer a spurious subdirectory of css/, we don't
     # need it any more.
-    find . -iname _\*.pcss | fgrep -v _components.pcss | LC_ALL=C sort |
+    #
+    # Exclude _sc/ folder dedicated for our own CSS files from being included
+    # to alphabetic sorting which causes cascading mess. Please note that CSS files
+    # inside the folder should be imported manually.
+    find . -iname _\*.pcss -not -path "./_sc/*" | fgrep -v _components.pcss | LC_ALL=C sort |
         while read i; do
             echo "@import \"$i\";"
         done
+
+        # After the alphabetic sort conducted above, import the CSS file dedicated
+        # for customization to let declarations on the file override the styles
+        # specified by the upstream project.
+        echo "\n/* Customization for SchildiChat */"
+        echo "@import \"./_sc/_customization.pcss\";"
 } > _components.pcss