The color of bubble and size of chat box

Hi, there.

Our company has been using the free plan and the chatting system works well.
I would like to change the color of the bubble( right now it is blue) which is the iron to start to chat. In addition to that, I would like to change the size of the chatbox. Now the box is too big for our website, so I really want to make it smaller.

If someone knows how to change those, please let me know. Or If I can not change those with the free plan, please let me know too.

Thank you.

Yuji