The installation instructions for the Aurora style are included in the .zip file.
1. Upload the contents of the upload directory into the styles folder located in 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 Choose File button and select the style-Aurora.xml file.
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To install any of the child themes (like Aurora Fluid) use ONLY step 2 and 3 above and select the theme from the child_themes folder.
Please make sure you specify Aurora as the PARENT theme!
Note: For the child themes YOU DO NOT need anything else other than the child theme xml files.
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Enjoy Aurora!