Applying css or manipulating and DOM elements of office js dialoque

I want to increase the height of div inside the div with class=ms-Dialog-content content_49e4f91a which is present inside the iframe .

Is there any way to apply css inside an office.js dialog?

Please suggest.Thanks.

The syntax for selecting the first element within another element by class, would be document.getElementsByClassName({class-name}).firstChild.

I'm not clear on the scenario you're trying to execute here but I am a bit concerned based on the screenshot. I can see an iframe under the div you're asking about. If you're attempting to set the height of a dialog created using the Dialog API, this should be specified when you call displayDialogAsync().