Nitrogen is the 4th free XenForo style designed by Brivium, that clean, modern and fresh.
LIVE DEMO: http://brivium.com/demo/Nitrogen/
1. Upload the contents of the upload directory to the root of your XenForo installation.
2. Go into your XenForo Admin Control Panel, click on Styles, and then click on "Import a Style" in the left-hand navigation list.
3. Click on the upload file field, and then navigate to and select the style-Nitrogen.xml file.