CSS child changes for the header don't work

Gday

I have been modifying my blog heavily using a style.css child theme for twenty twelve.

So far I have instituted changes for the body and for the header. Everything was working until I started to switch around widgets for the sidebar. Then, mysteriously, the changes for the header vanished but the ones for the body remained. How can I fix this?

Thanks for your help

Here is my blog – https://onandoffthegringotrail.com – and here is the css code:

[no need to post CSS – it’s all visible on your site]