styles: Rename night_mode.css to dark_theme.css.

Fixes part of zulip#20228.

Author: sahil839

postcss.config.js

@@ -6,7 +6,7 @@ const {media_breakpoints} = require("./static/js/css_variables");
 
 module.exports = ({file}) => ({
     plugins: [
-        (file.basename ?? path.basename(file)) === "night_mode.css" &&
+        (file.basename ?? path.basename(file)) === "dark_theme.css" &&
             // Add postcss-import plugin with postcss-prefixwrap to handle
             // the flatpickr dark theme. We do this because flatpickr themes
             // are not scoped. See https://github.com/flatpickr/flatpickr/issues/2168.

static/js/bundles/app.js

@@ -51,7 +51,7 @@ import "../../styles/popovers.css";
 import "../../styles/recent_topics.css";
 import "../../styles/typing_notifications.css";
 import "../../styles/hotspots.css";
-import "../../styles/night_mode.css";
+import "../../styles/dark_theme.css";
 import "../../styles/user_status.css";
 import "../../styles/widgets.css";