Phosphorus is the 9th free XenForo style designed by Brivium, that flat, modern and simple.
LIVE DEMO: http://brivium.com/demo/phosphorus/
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-phosphorus.xml file.