Change custom button color in Shipments screen

Hi community,
I am trying to apply custom styling (background-color and font-weight) to a custom action button on the Shipments (SO302000) screen header in the Modern UI.

Here is my code for the Classic UI:

 

        #region Actions
        public PXAction<SOShipment> bZProcessShipment;

        [PXButton(Category = "Processing")]
        [PXUIField(DisplayName = "Process Shipment", MapEnableRights = PXCacheRights.Select, MapViewRights = PXCacheRights.Select)]
        // Upgraded to Acumatica 2025 R2 by Biz_Vahe
        protected IEnumerable BZProcessShipment(PXAdapter adapter)
        {
            string shipmentNbr = Base.Document.Current?.ShipmentNbr;
            if (string.IsNullOrEmpty(shipmentNbr))
                return adapter.Get();

            var adapterCopy = adapter;

            Base.Save.Press();

            PXLongOperation.StartOperation(this, () =>
            {
                var shipmentGraph = PXGraph.CreateInstance<SOShipmentEntry>();
                //PXGraph sourceGraph = shipmentGraph.GetOrigDocumentGraph(string.Empty);
                var orderEntry = PXGraph.CreateInstance<SOOrderEntry>();


                SOShipment shipment = PXSelect<SOShipment,
                    Where<SOShipment.shipmentNbr, Equal<Required<SOShipment.shipmentNbr>>>>
                    .Select(shipmentGraph, shipmentNbr);

                if (shipment == null)
                    throw new PXException(Messages.ShipmentNotFound, shipmentNbr);

                #region Confirm Shipment
                shipmentGraph.GetExtension<ConfirmShipmentExtension>().PrepareShipmentForConfirmation(shipment);
                if (shipment.Confirmed != true)
                {

                    shipmentGraph.ShipPackages(shipment);
                    shipmentGraph.GetExtension<ConfirmShipmentExtension>().ConfirmShipment(new ConfirmShipmentArgs(shipment, orderEntry, true));
                }
                #endregion

                #region Email Shipment
                var parameters = new Dictionary<string, string>
                {
                    ["SOShipment.ShipmentNbr"] = shipment.ShipmentNbr
                };

                var branch = PXSelectReadonly2<PX.Objects.GL.Branch,
                    InnerJoin<INSite, On<INSite.branchID, Equal<PX.Objects.GL.Branch.branchID>>>,
                    Where<INSite.siteID, Equal<Required<SOShipment.destinationSiteID>>,
                        And<Required<SOShipment.shipmentType>, Equal<SOShipmentType.transfer>,
                        Or<INSite.siteID, Equal<Required<SOShipment.siteID>>,
                        And<Required<SOShipment.shipmentType>, NotEqual<SOShipmentType.transfer>>>>>>
                    .SelectSingleBound(shipmentGraph, null,
                        shipment.DestinationSiteID, shipment.ShipmentType,
                        shipment.SiteID, shipment.ShipmentType);

                shipmentGraph
                    .GetExtension<SOShipmentEntry_ActivityDetailsExt>()
                    .SendNotification(ARNotificationSource.Customer, "SHIPMENT", shipmentGraph.Accessinfo.BranchID, parameters, false);
                #endregion

                #region Print Labels
                var labelsPrintingExt = shipmentGraph.GetExtension<LabelsPrinting>();

                labelsPrintingExt.PrintCarrierLabels();
                #endregion

                #region Print Shipment Confirmation
                shipmentGraph.Report(adapterCopy.Apply(it => it.Menu = "Print Shipment Confirmation"), "SO642000");
                #endregion
            });

            return adapter.Get();
        }
        #endregion

<px:PXJavaScript runat="server" ID="CstJavaScript2" IsStartupScript="True" Script="function setActionButtonColor() {     var btn = document.getElementById("ctl00_phDS_ds_ToolBar_BZProcessShipment&quot;);     if (btn) {         btn.style.backgroundColor = &quot;#ffff00&quot;;         btn.style.color = &quot;#87b745&quot;;         btn.style.fontWeight = &quot;bold&quot;;     } }" />
            <px:PXLayoutRule runat="server" ColumnSpan="2" StartRow="true" LabelsWidth="S" ></px:PXLayoutRule>