How to apply transition to .button-native::after

I need to add transition to background-color of ion-button.
My css:
–transition: all 2s ease-in-out; → only have transition on text color

Transition on background color only works when I directly added transition: all 2s ease-in-out; to .button-native::after in dev tool.

I try to copy the CSS from dev tool to my css file but it doesnt work.
I did try:
ion-button::part(native)::after {
transition: all 5s ease-in-out !important;

But still, it doesnt work.
What should I do to have transition on background color of button