Make CSS Hot-reload work in a hacky way

src/vector/devcss.ts

@@ -0,0 +1,33 @@
+/*
+Copyright 2021 The Matrix.org Foundation C.I.C.
+
+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.
+*/
+
+/**
+ * This code will be autoremoved on production builds.
+ * The purpose of this code is that the webpack's `string-replace-loader`
+ * pretty much search for this string in this specific file and replaces it
+ * like a macro before any previous compilations, which allows us to inject
+ * some css requires statements that are specific to the themes we have turned
+ * on by ourselves. Without that very specific workaround, webpack would just
+ * import all the CSSes, which would make the whole thing useless, as on my
+ * machine with i9 the recompilation for all themes turned ou would take way
+ * over 30s, which is definitely too high for nice css reloads speed.
+ *
+ * For more details, see webpack.config.js:184 (string-replace-loader)
+ */
+if (process.env.NODE_ENV === 'development') {
+    "use theming";
+}
+