In the style.css file in your child directory, remove all the remaining content below the commented headers and have the first line (after the commented header lines) as
You can overwrite and existing styles or create new style classes in your child css file.
[quote]Note on the @import rule (from codex)
There must be no other CSS rules above the @import rule. If you put other rules above it, it will be invalidated and the stylesheet of the parent will not be imported.[/quote]
That probably means, your import should be the first statement in your child theme (below the template header) and may be only one import allowed in the file.