fix(styles): enforce styles for 5.1 release

Releated to #3025

client/src/app/App-patch.css

@@ -0,0 +1,28 @@
+.bio-properties-panel-group-header {
+  background-color: transparent !important;
+  position: relative !important;
+}
+
+.bio-properties-panel-group-header.open {
+  border-bottom: none !important;
+}
+
+.bio-properties-panel-applied-template-button .bio-properties-panel-group-header-button, 
+.bio-properties-panel-template-update-available .bio-properties-panel-group-header-button, 
+.bio-properties-panel-group-header-button.bio-properties-panel-select-template-button {
+  background-color: var(--select-template-background-color) !important;
+}
+
+.bio-properties-panel-applied-template-button .bio-properties-panel-group-header-button:hover, 
+.bio-properties-panel-template-update-available .bio-properties-panel-group-header-button:hover, 
+.bio-properties-panel-group-header-button.bio-properties-panel-select-template-button:hover {
+  background-color: var(--select-template-hover-background-color) !important;
+}
+
+.bio-properties-panel-template-not-found .bio-properties-panel-group-header-button {
+  background-color: var(--unknown-template-background-color) !important;
+}
+
+.bio-properties-panel-template-not-found .bio-properties-panel-group-header-button:hover {
+  background-color: var(--unknown-template-hover-background-color) !important;
+}

client/src/app/App.js

@@ -62,6 +62,9 @@ import { PluginsRoot } from './plugins';
 
 import css from './App.less';
 
+// monkey-patch to fix styling issues ahead of release 5.1, tracked here https://github.com/camunda/camunda-modeler/issues/3025
+import './App-patch.css';
+
 import Notifications, { NOTIFICATION_TYPES } from './notifications';