How to customize the event calendar's flyout box

Hi!

I tried some CSS codes to edit the event calendar without getting it as I wished. When the browser window is small the website looks almost as I wish. When I increase the window size to full screen the whole look of the calendar changes and the flyout item is getting back to gray. Is this possible to change somehow that the box is acting always the same way (like on the picture with green flyout box).

It would be nice if the flyout item would be all the time greenish as on the other picture. The green box is also a little bit too big compared to the text. See the empty space left and right. Is is possible to make smaller that the box is following the size of the text?

I would be super glad for the help 🙂
Here's the website: https://www.soulskintattoo.com/eventscalendar

Add this to Website Tools > Custom CSS to make box smaller

.flyoutitemlist {
    height: auto !important;
}