GZIP seems to compress only HTML, not CSS or JavaScript
You can use .htaccess config from HTML Boilerplate for better configuration. There are a lot of useful config option there.

I use this config to enable gzip compression in my personal blog, and it's worked perfectly.

&lt;IfModule mod_deflate.c&gt;

    # Force compression for mangled `Accept-Encoding` request headers
    &lt;IfModule mod_setenvif.c&gt;
        &lt;IfModule mod_headers.c&gt;
            SetEnvIfNoCase ^(Accept-EncodXng|X-cept-Encoding|X{15}|~{15}|-{15})$ ^((gzip|deflate)\s*,?\s*)+|[X~-]{4,13}$ HAVE_Accept-Encoding
            RequestHeader append Accept-Encoding "gzip,deflate" env=HAVE_Accept-Encoding
        &lt;/IfModule&gt;
    &lt;/IfModule&gt;


    # Compress all output labeled with one of the following media types.
    &lt;IfModule mod_filter.c&gt;
        AddOutputFilterByType DEFLATE "application/atom+xml" \
                                      "application/javascript" \
                                      "application/json" \
                                      "application/ld+json" \
                                      "application/manifest+json" \
                                      "application/rdf+xml" \
                                      "application/rss+xml" \
                                      "application/schema+json" \
                                      "application/vnd.geo+json" \
                                      "application/vnd.ms-fontobject" \
                                      "application/x-font-ttf" \
                                      "application/x-javascript" \
                                      "application/x-web-app-manifest+json" \
                                      "application/xhtml+xml" \
                                      "application/xml" \
                                      "font/eot" \
                                      "font/opentype" \
                                      "image/bmp" \
                                      "image/svg+xml" \
                                      "image/vnd.microsoft.icon" \
                                      "image/x-icon" \
                                      "text/cache-manifest" \
                                      "text/css" \
                                      "text/html" \
                                      "text/javascript" \
                                      "text/plain" \
                                      "text/vcard" \
                                      "text/vnd.rim.location.xloc" \
                                      "text/vtt" \
                                      "text/x-component" \
                                      "text/x-cross-domain-policy" \
                                      "text/xml"

    &lt;/IfModule&gt;

    &lt;IfModule mod_mime.c&gt;
        AddEncoding gzip              svgz
    &lt;/IfModule&gt;

&lt;/IfModule&gt;