need help changing theme after creating css

I created a folder.  Change my css to give me the look I want.

I added this folder to the app_themes folder.
Now I am trying to select this theme using the admin configuration and do not see it.

Where is it.  Is it global or all settings?  How do I find it.

And once I find it then all I need to do is change the   <pages theme="DarkOrange"> to be
<pages theme="myCss">

Is that correct?

Thanks Howard

I found it.  I change it there and it worked.

Do I need to change the <pages theme="DarkOrange">

Configuration --> Global Settings --> Seo/Display --> Store Theme

That is the only thing you need to change.