LeafWeb/WebCms/Views/Shared/DisplayTemplates/_ViewDataCssClass.cshtml

@using System.Collections
@{
    // pass in class name via the cssClass key in ViewData
    if (ViewData.ContainsKey("cssClass"))
    {
        var cssClasses = (string[])ViewData["cssClass"];
        <text>class="@string.Join(" ", cssClasses)"</text>
    }
}