Solution for Ionic v4
For so many time i was trying to push some cssStyle to the ion-alert and today was the day.
Normally i was trying to do this:
But after hour trying to make it works, i decide to change the exactly the css name of the alert and put the style in variables.scss.
In my case.
For header the class was: .alert-title.sc-ion-alert-md
For the non-selected options was: .alert-radio-label.sc-ion-alert-md
And For the selected option was: [aria-checked=true].sc-ion-alert-md .alert-radio-label.sc-ion-alert-md
Maybe is not the best way to made it, but works really good