cannot set modal backdrop root element

Created by: eladmarg

after modal backdrop change, it's always appended to the body.

there is a constructor to change the default, but it always taking default values for visible and animated properties. return new Backdrop({ isVisible: Boolean(this._config.backdrop), isAnimated: this._isAnimated(), });

so even if this._config contains other parameters, they're not passed to the ctor. this can be extended with ... or get other properties as well.