How to apply border to ion-grid

Ionic Framework ionic-v3
1

May I know how to apply border to ion-grid? I tried as in scss as below, but failed.

ion-col {
border: think solid black;
}

2

Make sure the file for the page is being loading in the app.core.scss file. This is a typical issue when styles aren’t getting applied.

3

I had added into app.core.scss as below

@import "../pages/mypage/mypage";