You can add your own overlays to Street Smart. From the Dashboard, choose Layers and click Add custom layer. You can choose between WFS, WMS and shape overlays. Also you can add an SLD (styling) file with a WFS server inside.
When you add a WFS or WMS you will be asked to give the URL, optional parameters, version and if you want to use an proxy or username and password. After checking the available layers you can choose the styling of the layer.
For the shape file you browse to a zipped shapefile and open it to add it to Street Smart. After adding the shape you can choose the styling of the shape file.
When adding a SLD with WFS inside it will be shown in the correct styling directly. For building SLD files read the documentation at the website.
After the layer has been added you can change the style in the layer list. From the Dashboard, choose Layers and select the editing button from the layer. Depending on the the type of layer, you can edit different style elements.