This is possible 🌝
When adding an Image to the Gridder, you can 'right-click' either the Element or the Row and set an "HTML Class or ID" :
In the example above I have filled the row with my desired image and given it the custom Class name "special".
Customize > CSS
Lay Options > Custom CSS & HTML > Custom CSS
I have added the following code:
This targets the row with the class "special" and tells the Image inside to follow these CSS Rules.
Now the result:
This Image of Clouds will remain in the background as i scroll up and down the page and keep a width of '100vw' ( 100% of the browser's viewport width).
You may wish to add the CSS 'z-index' property to the above code if certain elements are hidden behind your image:
Additional link that may aid you:
Best wishes Charley and hope this helps you, Thank you for the kind words about Lay Theme and good luck! ✨