Q:

Ionic 3 Changing ion card header padding is not overriding the existing one

I am trying to override existing sass styling of ion-card, by changing the headers padding to something that fit my app. 
I did the following:
ion-card-header{
  .card-header-md{
    padding-right: 20px ! important;
    padding-left: 16px ! important;
    padding-top: 16px ! important;
    padding-bottom: 16px ! important;
  }
}

But nothing changed.  I tried to add a background color to check it is getting the styling:
ion-card-header{
  color: red;
  .card-header-md{
    padding-right: 20px ! important;
    padding-left: 16px ! important;
    padding-top: 16px ! important;
    padding-bottom: 16px ! important;
  }
}

And the color changed to red.  But the card-header-md is not changing.  I need to change it on iOS and Android. 
Here is a stackblitz for it. 

A:

The issue is that the card-header-md class is at the same level as the ion-card-header class.  So this should work:
ion-card-header {
  &.card-header-md {
    padding-right: 20px
    padding-left: 16px;
    padding-top: 16px;
    padding-bottom: 16px;
  }
}

I've removed the ! important because I think you don't actually need them (just tried in a new stackblitz demo and it's working fine without them).