Add classname to Interact dropdown widget

I am using Interact (Blink) - I create a dropdown widget

 ddl = dropdown(Observable(attr_values));

I would like to add “loader is-active” classname to the Select … when a value is selected and remove when the data comes back from DB. How?

I was hoping for something like this

ddl[:attributes] = "loader is-active"

Is it possble ?

for a button I use