Hi Paul

Do you have other settings established for the 'class' key? if so then yes I don't think it's clever enough to merge them...

... what you could do (and it's a bit hacky) is update the RenderElementAttributes method of your grid renderer file, to look for your 'other properties' and combine them into any 'class' attribute that might have already been applied: (I have a hacky example below... I saw once on a project and I'm not saying 'replace' is the best way to merge the css classes but hopefully it gives you a hint of how you might achieve it)

public static MvcHtmlString RenderElementAttributes(dynamic contentItem,bool isCustomRow)
    {
        var attrs = new List<string>();
        JObject cfg = contentItem.config;
        bool hasCssClass = false;
        bool hasBackgroundImage = false;

        if (cfg != null)
        {
            foreach (JProperty property in cfg.Properties())
            {
                var propertyValue = HttpUtility.HtmlAttributeEncode(property.Value.ToString());
                attrs.Add(property.Name + "=\"" + propertyValue + "\"");
                if (!hasCssClass)
                {
                    hasCssClass = property.Name == "class";
                }

            }
        }


        JObject style = contentItem.styles;

        if (style != null)
        {
            var cssVals = new List<string>();
            foreach (JProperty property in style.Properties())
            {
                var propertyValue = property.Value.ToString();
                if (string.IsNullOrWhiteSpace(propertyValue) == false)
                {
                    if (property.Name == "background-image")
                    {
                        hasBackgroundImage = true;
                    }
                    cssVals.Add(property.Name + ":" + propertyValue + ";");
                }
            }

            if (cssVals.Any())
            {
                attrs.Add("style=\"" + HttpUtility.HtmlAttributeEncode(string.Join(" ", cssVals)) + "\"");
            }
            if (hasBackgroundImage)
            {
                if (hasCssClass)
                {
                    int classIndex = attrs.FindIndex(f => f.Contains("class="));
                    attrs[classIndex] = attrs[classIndex].Replace("class=\"","class=\"background-image-row icons-row ");
                }
                else
                {
                    attrs.Add("class=\"background-image-row icons-row \"");
                    hasCssClass = true;
                }
            }
        }
        if (isCustomRow)
        {
            if (hasCssClass)
            {
                int classIndex = attrs.FindIndex(f => f.Contains("class="));
                attrs[classIndex] = attrs[classIndex].Replace("class=\"", "class=\"custom-row ");
            }
            else
            {
                attrs.Add("class=\"custom-row \"");
                hasCssClass = true;
            }
        }
        return new MvcHtmlString(string.Join(" ", attrs));
    }