Cool, good to hear.
1) As far as I can tell there is no standard way to get battery info in a browser. The existing API is deprecated and will be removed.
https://developer.mozilla.org/en-US/...BatteryManager
2) What you are using is fine, to make it more geenral use
* { font-weight: bolder !important; }
3) You can add whatever colors you like when highlighting