I would like to leave my solution simplified, for the next people who have this situation.
I found that the div element is generated using javascript. Therefore, it is necessary to use javascript to change these properties only after the pop-up is generated.
And since the pop-up is inside an iframe, one solution is to insert something like this piece of jquery in an xy expression in the pop-up:
$ (document) .ready (function () {
$ ('# "+ btnMax.Id +"'). click (function () {
$ ('. os-internal-Popup', window.parent.document) .css ('top', '0px');
$ ('os-internal-Popup', window.parent.document) .css ('cor de fundo', '# e6e6e6');
});
});
Thank u!