Gzip compressed css file with php header, first css line does not work

I am using gzip to compress my files so I need to add the following code to the top.

ob_start("ob_gzhandler");
header("content-type: text/css; charset: UTF-8");
header("cache-control: must-revalidate");
header("expires: ".gmdate('D, d M Y H:i:s', time() + 1000)." GMT"); 
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The problem is now that the first line of css code in my file does not work. e.g.

body{
  color: red;
  font-weight: bold;
}
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using this the text would be bold but not red.

Looking forward to an advice.

Thanks in advance.