CSS class not applied in MVC

<div class="form-group">
    @Html.LabelFor(model => model.RollNo, new { Class = "col-sm-3 control-label" })
    <div class="col-sm-9">
        @Html.EditorFor(model => model.RollNo, new { Class = "form-control",placeholder = "Large input" })
        @Html.ValidationMessageFor(model => model.RollNo)
    </div>
</div>

I have generated above MVC view using Entity framework.I want to apply css class for the html control.

But CSS is not applied.Later i identified the correct option @HTML.EditorFor is not suitable for the css class.

FInally i appplied the correct option i.e

@Html.TextBoxFor(model => model.RollNo, new { Class = "form-control", placeholder = "Large input" })

<div class="form-group">
    @Html.LabelFor(model => model.RollNo, new { Class = "col-sm-3 control-label" })
    <div class="col-sm-9">
        @Html.TextBoxFor(model => model.RollNo, new { Class = "form-control",placeholder = "Large input" })
        @Html.ValidationMessageFor(model => model.RollNo)
    </div>