[EuiButtonGroup] Selected, focus and hover buttons in a compressed are identical with Amsterdam themes

[jpambrun]

Selected, focus and hover buttons in a compressed button are identical with Amsterdam themes. In multi-selection mode, it makes it impossible to know the state of the last toggled button as it become focuses.

In the following example 'US" was just toggled 'OFF' :

[cchaos]

Thanks and 👋 welcome @jpambrun! Amsterdam is still being developed and consider quite a few components to still be a little broken. We've got a larger roadmap you can track to keep up to date with the status here: #2639

EUI folks, I've got this one covered in my work on the accessibility of the EuiButtonGroup.