Chrome renders semi-transparent overlays as a black screen

After the latest Chrome update, the semi-transparent overlay that GeneXus displays when we click a button and lasts while that button completes the process, on many PCs, instead of being a semi-transparent gray background, turns the entire screen black until the process completes.

I assume Chrome changed how it renders semi-transparent overlays, and in certain desktop environments it's not applying transparency, displaying solid black. How can I explicitly change it in GeneXus to gray and return to the effect it had before?

I use GeneXus 15, C#, web.

I've learned that one option is to add it from GeneXus to the Theme CSS or the Master Page, but I don't know how to do it. Something like:

.gx-mask {
  background-color: rgba(128, 128, 128, 0.5) !important; /* gris semitransparente */
  opacity: 1 !important; /* evita que Chrome interprete mal */
}

In order to change this, you need to open the Theme Object defined in the property Default Theme of your KB in Preferences. Once opened, look in the folder Customs for the class DIV.gx-mask:

There you can edit the class properties on the right pane tab Properties, for example:

If you need to add !important properties, go to the last property "Custom properties" and there you can add:

background-color: rgba(128, 128, 128, 0.5) !important; opacity: 1 !important;