very simple twentyeleven child doesn't work

It’s about as simple as can be, and all of the formatting from 2011 fails to come over when I use the child. Here’s what I have in style.css:

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/*
Theme Name:     Twenty Eleven Child
Template:       twentyeleven
*/
@import url("../twentyeleven/style.css");

I have played around with whitespace, forcing the full URL, encoding, you name it – but no result.

Your help is much appreciated