At Nikeo's suggestion, here's a post with lots of CSS snippets that you can use in a child theme to modify aspects of Customizr. They are tested--by me (a newbie!)--with Customizr 3.0.2 and WP 3.5.2.
I hope that this can become a repository for tried-and-tested CSS snippets that work with Customizr---so we don't have to keep re-posting CSS snippets / answers to common questions, but can simply point here instead.
Please feel free to add your own snippets that work, using the
code backticks and with comments to say what they do. Please open separate threads if you want to discuss a particular code snippet in detail, rather than clog up this thread.
[CSS moderated. Please don't post that much CSS here.]