1) Transparent Header:
To create a transparent header using Header Builder, simply add a row to the canvas. Click on the row to see its settings. In the settings ensure that the opacity of the background color is set to 0.
Now, click on the settings icon from the left panel and enable Overlapping Content option.
The above steps will create a transparent header for you on any page.
2) About Overlapping Content option for each device, I have noted this request. If the dev’s see this request fit, it will be added to the Header Builder in the future releases.