Relation Manager Form - Adjust size/width

Is it possible to adjust Relation Manager Form size? Have a big screen and form modal width is about 50% screen width.

I have tried to use

$form->extraAttributes(['style' => 'width: 100%'])

$form->extraAttributes(['style' => 'width: 100%'])

or add custom class the same way, but neither style or class does not appear at form container div.