Hydrogen is a clean, mordem style, designed by Brivium LLC, it supports all of XenForo's rich styling features, including Style Properties.
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-Hydrogen.xml file.