I want to add custom chrome for my modules, and I'd like to take peek at source of standard chrome styles in Joomla but I can't find their location.
If anyone can help it's much appreciated.
To override those defaults you just need to place a file called modules.php in a folder called html in your template, e.g.:
/templates/[your default template]/html/modules.php.
Then you can apply your custom module chrome either by specifying it in index.php of your template or within the module settings.