Navigate to Confluence administration → Linchpin Theme → Configuration.
At the very top of the page you should see a yellow warning box.
Inside this yellow box, you can find an Activate theme button. Click on the Activate theme button.
Now Linchpin Theme should be active on your Confluence instance.
You can manually look up if Linchpin Theme is activated on your system.
To verify that Linchpin Theme is active, navigate to Confluence administration → Look And Feel → Themes.
Make sure that Linchpin Theme (green icon) is selected.
If Linchpin Theme is not active, click on the Linchpin Theme (green icon) button to select Linchpin Theme. Then, click on the Confirm button.
Link to this page: https://seibert.biz/activatelinchpintheme