feature(dark mode): misc design fixes (#2215)

* Fix category dark mode styles

* Fix sidebar account tab states

* Fix dashboard balance sheet group styles

* Fix budget dark mode styles

* Fix chart gradient split

* Fix prose styles in dark mode

* Add back chat nav id for tests

app/javascript/controllers/sidebar_tabs_controller.js

@@ -0,0 +1,16 @@
+import { Controller } from "@hotwired/stimulus";
+
+// Connects to data-controller="sidebar-tabs"
+export default class extends Controller {
+  static targets = ["account"];
+
+  select(event) {
+    this.accountTargets.forEach((account) => {
+      if (account.contains(event.target)) {
+        account.classList.add("bg-container");
+      } else {
+        account.classList.remove("bg-container");
+      }
+    });
+  }
+}