how to download a css file from a style string in asp.net web api

Your return object is likely using one or both of the IDisposable objects, but disposing of them shortly you return (by way of the using statements).

Manage your memory differently - make calls to stream.Dispose() and httpResponseMessage.Dispose() manually where appropriate - maybe in your class destructor, though in my experience HttpResponseMessage doesn't need disposing as it's dealt with by the garbage collector once you've finished working with it. Example code:

``` byte[] textAsBytes = Encoding.Unicode.GetBytes(concatenatedStyles);

        using(MemoryStream stream = new MemoryStream(textAsBytes)) {
            var httpResponseMessage = new HttpResponseMessage(HttpStatusCode.OK);
            httpResponseMessage.Content = new StreamContent(stream);
            httpResponseMessage.Content.Headers.ContentDisposition = new ContentDispositionHeaderValue("attachment") {
                FileName = "main-theme.scss"
            };
            httpResponseMessage.Content.Headers.ContentType = new MediaTypeHeaderValue("text/css");

            return ResponseMessage(httpResponseMessage);
        }

```

You might need to remove the using around the MemoryStream too, I'm not 100% sure as I can't compile your code on my system.

ResponseMessageResult responseMessageResult;

using (MemoryStream stream = new MemoryStream(textAsBytes))
using (HttpResponseMessage httpResponseMessage = new HttpResponseMessage(HttpStatusCode.OK))
{
    httpResponseMessage.Content = new StreamContent(stream);
    httpResponseMessage.Content.Headers.ContentDisposition = new ContentDispositionHeaderValue("attachment")
    {
        FileName = "main-theme.scss"
    };
    httpResponseMessage.Content.Headers.ContentType = new MediaTypeHeaderValue("text/css");

    responseMessageResult = ResponseMessage(httpResponseMessage);
}

return responseMessageResult;