Input file not passed to asp.net core using form

Question

I am having form like this:

<form action="/Art/Add" type="POST">
    <input type="text" name="ddd" value="testttt" />
    <input type="file" name="files" />
    <button>Add</button>
</form>

Then i submit file to it and submit form and header looks something like this (it has more data than shown here)

And here is the server side code:

[Route("/Art/Add")]
public IActionResult Add(TempArtClass artModel)
{
    JsonResult t = base.ImageUpload(artModel.files).Result as JsonResult;
    string[] fullFilePathsReturned = t.Value as string[];

    User<UserCustomProperties> cu = Request.GetUser();

    if (cu == null)
        return View("Error", "You do not have permission to add new art!");

    if (string.IsNullOrWhiteSpace(artModel.art.Name))
        return View("Error", "You must enter name!");

    if (artModel.art.Name.Length > 32)
        return View("Error", "Name must not exceed 32px!");

    Art<ArtInformation>.Add(artModel.art.Name, cu.ID, artModel.art.Price, artModel.art.Details, artModel.art.VAT, fullFilePathsReturned[0], artModel.art.Type, artModel.art.Tag);

    return Redirect("/" + cu.Name + "/a/" + artModel.art.Name);
}

TempArtClass is this:

public class TempArtClass
{
    public Art<ArtInformation> art { get; set; }
    public List<IFormFile> files { get; set; }
    public string ddd { get; set; }
}

and when i debug ddd has value, art class has value but my files is null.... I also tried adding multiple to html tag <input> but it is not working.