How to use Ionic's default theme CSS variables

I’d like to use some of the default Ionic theme color variables like --ion-border-color, --ion-color-step-200 etc in my application. I notice several of these are defined in src/theme/variables.css for dark mode but not for the default :root selector. So for example if I set an icon’s color like below the style takes effect in dark mode but not in the default light mode.

.my_icon {
	color: var(--ion-color-step-200);

Am I missing the proper method for using Ionic’s default theme CSS variables?