When css and js are compressed, they are returned to the browser which should unzip them. But when it fails, css design is broken. To fix that follow this : 

Edit settings.php and uncomment the lines : 

$conf[‘css_gzip_compression’] = FALSE;
$conf[‘js_gzip_compression’] = FALSE;

Edit .htaccess and delete this call : 

<IfModule mod_headers.c>

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