If you want to override the default website interface style sheets and templates, here is one method of acheiving it.

Create the following structure in the extension directory:

ezwebin_custom
| - design
| | - ezwebin_custom
| | | - images
| | | - override
| | | | - templates
| | | - stylesheets
| | | - templates
| - settings

In the extension/ezwebin_custom/settings directory create a file called design.ini.append.php with the following content:

<?php /*
[ExtensionSettings]
DesignExtensions[]=ezwebin_custom
*/ ?>

Edit settings/override/site.ini.append.php file and add this into the [ExtensionSettings] block:

ActiveExtensions[]=ezwebin_custom
Note that ezwebin_custom must be placed BEFORE ezwebin to override it. For example like:

[ExtensionSettings]
ActiveExtensions[]=ezodf
ActiveExtensions[]=ezdhtml
ActiveExtensions[]=ezwebin_custom
ActiveExtensions[]=ezwebin

Edit the [DesignSettings] block of settings/siteacees/your_default_site_access so that the default SiteDesign matches the name of the design folder in your new extension e.g. design/ezwebin_custom would require setting SiteDesign=ezwebin_custom. Also make sure ezwebin is added to the AdditionalSiteDesignList. Example:

[DesignSettings]
SiteDesign=ezwebin_custom
AdditionalSiteDesignList[]=base
AdditionalSiteDesignList[]=ezwebin

Copy stylesheets from 'extension/ezwebin/design/ezwebin/stylesheets' to your custom design extension 'extension/ezwebin_custom/design/ezwebin/stylesheets'. Edit these to make style shanges.

You should now be able to create system and override templates as you would be used to in previous versions, except you will now be working in the extension/ezwebin_custom/design/ezwebin_custom directory rather than design/your_site_access/.

Class and template editing are disabled by default since the 3.9.0 release. A solution to this problem is to modify SiteAccessRules to allow advanced editing.