How to set scroll bar's color of IonContent for dark mode?

I’d like to make the color of the scroll bar in IonContent to be black (at least dark) in dark mode because contents are bright.
However, in dark mode, the scroll bar of the IonContent is always white.

I set the meta tag of the color-scheme to be light to make my app just as same as in the light mode although the user set the device in dark mode. But it didn’t work.

<meta name="color-scheme" content="light" />

What should I do?
Please give some help.