Battery Icon flaw

[kirakishima]

Describe the bug
The inside of battery-level-XX-charging-symbolic does not change color with styles on many gtk themes (including default Adwaita).

To Reproduce
Steps to reproduce the behavior:

1. Add a battery-charging icon to the window.

const battery = await Service.import("battery");

const icon = Utils.merge([battery.bind("percent"), battery.bind("charging")], (p, c) => {
  return `battery-level-${Math.floor(p / 10) * 10}${c ? '-charging' : ''}-symbolic`;
})


export default () => Widget.Box({
  className: "battery-indicator",
  visible: battery.bind("available"),
  children: [
    Widget.Icon({
      className: "battery-icon",
      icon: icon
    }),
    Widget.Label({
      label: battery.bind("percent").as(p => `${Math.floor(p)}`)
    }),
  ],
});

2. Apply styles to battery icon

.battery-icon {
  color: red;
}

Expected behavior
The inside of the battery icon should be colored in the style color.

Screenshots

Desktop (please complete the following information):

• OS: Void Linux x86_64 glibc
• App: Ags
• Version: 1.8.2

Additional context
I tried different gtk icon themes and they all have the same thing, well besides the adwaita++ theme but I want to use the standard adwaita.