It's perfect to see current day has been marked with red background, how can I mark the holidays (say 12/25) with some background color also?
The documentation of the customization option
Non-nil means mark dates of holidays in the calendar window. The marking symbol is specified by the variable `calendar-holiday-marker'.
I suggest to enable this option. I've tested it with
emacs -Q and it works in emacs 25.3.1.
The screenshot after additionally adding
calendar-visible-today-hook and adapting
calendar-today face to your configuration: