Changing date pop-up alignment

Hi,

First of all, thank you for this great plugin! It really does what I needed and being able to adjust the look via CSS is especially nice.

However, I haven’t been able to make one change: because the calendar is in a sidebar on the right side, I need the event detail pop-up to go out towards the left of the date, instead of to the right of the date. Right now, it juts out to the right, beyond the sidebar, so that the details cannot be seen if the date is anywhere beyond the middle of the calendar (horizontally).

How can I make this adjustment? I tried various things in the CSS but none seemed to work.

Thanks in advance and, again, for the good work,
Ben

http://ww.wp.xz.cn/extend/plugins/blog-post-calendar-widget/