Is there not a theme repository ? I desperately need to change the default theme; I think it hinders me typing the wrong code in the wrong tab.

Ps. Why don’t I get email notifications ? I don’t see any option when I write a post or in my control panel.

There is not, but you can always extract it locally and edit in-place by either using an override package or by using the theme override mechanic of just placing same-named file somewhere, e.g. User folder.

Email notifications don’t work because there is no mail service.

There is no web site where I can see screen shots of themes ?

I’m not sure I understand, but if you’re talking about forum themes then there is only one:

I mean themes for Sublime, whereas I can preview all the themes available rather then download and not like and cycle over and over.

Most themes have Screenshots in their Readme, which is shown on packagecontrol.io.