Where did you get config.useDefaultSettings()? It’s not in the doc.
This is what I use. I cleanup the css, and define dialog styles in my app’s scss file.
config.useDefaults();
config.useCSS('');
BTW .useCSS('_dialog.scss') would not work, you need to pass a piece of css text to the call. But it looks like you should do the same thing I did, just load your _dialog.scss in app’s main css.
And thanks for the note that .useCSS('_dialog.scss') wouldn’t work. I totally overlooked the fact that the SASS would not be compiled. Or at least that I what I am assuming after reading your comment.
I have added the dialog styles to my base styles as you suggested. Thanks!