Make it easier to spot reaction buttons

In dark themes it can be very hard to spot the reaction
buttons when using compact mode. 

Before:

![image](/uploads/f499f5fd16be353c5fef9b1a08e99522/image.png)

After:

![image](https://invent.kde.org/network/neochat/uploads/86e6cecc546d73481dff79debdcadc3f/image.png)

Also this uses the given colorscheme so it will work everywhere 😄