Change Legend Window Background to be semi-transparent?

[TimHayes3]

How to adjust the background transparency of the Legend and Layer List Widgets windows? Currently the background color is set to white, but I would like to keep it white and make it 25% transparent. 

[Laura]

From what I see out the box you either get 100% transparency or 0%

[SteveCole]

You can probably target a specific CSS class to accomplish this but it would only work with a self hosted Developer edition version of EB

[TimHayes3]

When I used to use the WAB DE I was able to make it transparent. I am surprised that ESRI does not allow it out of the box using Experience Builder. I hope they respond to my question here. 

[Laura]

You can include it in the idea forum! But yes DE offers more flexibility. 

[Shen_Zhang]

You should be able to change the legend background transparency on Advanced -> background, but not for the Map layers widget.