Sorry - bad description - it's hard to keep it short
What I mean is that the "box shadow" css effect is used to indicate that if you click on an event - you will be able to create a new event on that day. The problem is that the day also has links to do other things (like view the details of an event) and the box-shadow is not removed when the cursor will do a different action. So it is misleading.
I looked and there is no simple CSS only solution - but there is a simple JS + CSS solution if we use a mouse over event handler to add a "hovered" class to the most specific element, and remove it from all other elements. This would allow us to determine the day is hovered, but none of it's child elements.