Changing Background Colour of Current Month in Calendar
 

I found this StyleVar to control the background of the days of the month in the Calendar for months other than the current month:

calendar_othermonth_background_color

However, what I'm trying to change is the background colour of the days of the current selected month.

vBulletin Support says that "this is not a simple change to make due to the way the CSS works for the calendar. This will require modifying the code (i.e., 'hacks', plugins, or template modifications)"

Anyone can help?