Tutorial is in the end of description.
This video will show you how to install and activate any Steam skin that you have downloaded, Thank you for watching.
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Top 5 Steam skins: https://www.youtube.com/watch?v=shvuI2KSCJ0
Air skin for Steam: http://steamskins.org/air-skin-for-steam/
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Tutorial:
Download the skin file below, you should get an archive with the “.zip” or “.rar” extension.
Extract the ZIP or RAR and move the folder to:
Windows: C:/Program Files (x86)/Steam/skins
MAC OS X: right-click Steam.app and choose show package contents then /Contents/MacOS/skins
Linux: ~/.local/share/Steam/skins/
Open the Steam interface and in top tab, click on “Steam” / “Settings”.
Then open the Interface section.
Find the option “Select the skin you wish Steam to use (requires Steam to restart)” and choose the skin that you want.
Completely shut down and restart Steam.
That was all; now you must have another interface.