Apply Jenkins theme via init script

services/jenkins/helmrelease.yaml

@@ -170,6 +170,23 @@ spec:
             println("Failed to configure OIDC realm: ${e}")
             throw e
           }
+        theme.groovy: |
+          import jenkins.model.Jenkins
+          import org.codefirst.SimpleThemeDecorator
+
+          def instance = Jenkins.get()
+          def decorators = instance.getExtensionList(SimpleThemeDecorator.class)
+
+          if (decorators?.size() > 0) {
+            def theme = decorators[0]
+            theme.setCssUrl("https://jenkins-contrib-themes.github.io/jenkins-material-theme/dist/material-ocean.css")
+            theme.setJsUrl("")
+            theme.setTheme("")
+            instance.save()
+            println("Applied simple-theme-plugin dark theme")
+          } else {
+            println("simple-theme-plugin not installed; skipping theme configuration")
+          }
       JCasC:
         defaultConfig: false
         securityRealm: ""
@@ -244,10 +261,6 @@ spec:
                 creationOfLegacyTokenEnabled: false
                 tokenGenerationOnCreationEnabled: false
                 usageStatisticsEnabled: true
-            unclassified:
-              simple-theme-plugin:
-                elements:
-                  - cssUrl: "https://jenkins-contrib-themes.github.io/jenkins-material-theme/dist/material-ocean.css"
           creds.yaml: |
             credentials:
               system: