Do you want to do these things specifically in Safari? Or across all browsers?
If you are at 100% width already, then you won’t be able to extend it any further without modification to your theme or by positioning the menu via absolute/relative positioning. You may also be able to extend it by using negative margins, but I’ve never tried this before so aren’t 100% certain.
There are many ways to move it. How you move it depends on where you are moving it to. Absolute/relative positioning are useful ways of doing this, although applying margins to manipulate into place may be more suitable in some circumstances.