dcc.Dropdown and data-dash-is-loading incompatibility

I’m using

    visibility: hidden;
    content: "Loading...";
    display: inline-block;
    color: magenta;
    visibility: visible;

in the CSS file without any problem.
But now I want to add a dcc.Dropdown using Dynamic Options
After trying for a while without success, I notice that this only works if I don’t use the data-dash-is-loading component.
Are they incompatible or I’m missing something.
Thanks in advance !!!