Wrong mime-type for css and js files

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http://serverfault.com – I am new to Apache. I have almost no knowledge of apache. I am using apache 2.2.11. I have one css file and multiple .js files which i am uploading to a remote storage with a php page(PHP - 5.2.8). When i am using function mime_content_type to get the mime type of css.css file, i am getting text/plain. Same issue with .js files. There are some image files for which mime-types returned are correct with the same function. I have checked that server has text/css css defined in mime.types file. The incorrect mime-type is creating issue for me and i have spent a lot of time with no success. Any (HowTos)