--background-hover on <ion-button> help please

Is anyone else having trouble with --background-hover on an <ion-button>? Seems other CSS custom properties work fine, but cannot seem to change the --background-hover.

My second question is should the --background-hover be changed on the button or on hover (see below)?

.button {--background-hover: blue}
.button:hover {--background-hover: blue}

Thanks in advance!

I have the same issue with @ionic/core: 4.7.4

turned out i didn’t use the color css variables correctly.
now using https://ionicframework.com/docs/theming/color-generator with all the needed css variables in them.