Here how to put skins on ao3!

In order to create a site skin, you need to have an AO3 account and you need to be logged in.

1. Copy the link of whatever skin you want you can find them on Reddit or Tumblr.
2 Sign into AO3 if you haven't already. At the top of the page, tap on your username.
3. From the dropdown menu that appears, tap on Dashboard.
4. On your Dashboard, tap on the link called Skins.
5. On the Skins page, tap on the button labelled Create Site Skin.
6. Give your site skin a unique title. I usually add my username or nickname to the end of my title in order to make it unique. You need a unique title in order to save your skin. IF YOUR SKIN NAME IS NOT UNIQUE, YOU WILL GET AN ERROR WHEN YOU TRY TO SAVE.
7. Paste the code into the CSS box of the new skin you are creating.
8. Afterwards, scroll to the bottom of the page and tap on the button labelled Submit. This will save your site skin and take you to a new page where you can see the title of your skin as well as all of the code.
9. On the site skin page, tap on the button labelled Use. You will now have this skin every time you're logged in on any device.