Set background color and adjust label positioning

Added a `BackColor` property to both `signature` and
`signatureLabel` objects to improve visual consistency.
Adjusted the `BoundsF` property of `signatureLabel` to
slightly move the label upward for better alignment.

EnvelopeGenerator.ReceiverUI/Pages/ReportViewer.razor

@@ -682,16 +682,18 @@ Shown="OnPopupShownAsync">
             Sizing      = ImageSizeMode.ZoomImage,
             Borders     = BorderSide.Bottom,
             BorderColor = System.Drawing.Color.FromArgb(73, 80, 87),
+            BackColor = Color.FromArgb(219, 219, 219)
         };
 
         var signatureLabel = new XRLabel {
             Name          = $"receiverSignatureLabel_{annotId}",
             Text          = signatureInformation,
             Multiline     = true,
-            BoundsF       = new RectangleF(sigX, labelY, sigWidth, infoHeight),
+            BoundsF       = new RectangleF(sigX, labelY - 5, sigWidth, infoHeight),
             Font          = new DXFont("Open Sans", 8F, DXFontStyle.Regular),
             ForeColor     = System.Drawing.Color.FromArgb(73, 80, 87),
             TextAlignment = TextAlignment.TopCenter,
+            BackColor = Color.FromArgb(219, 219, 219)
         };
 
         // Show each control only on the target page using an independent print counter