Since the spring of 2018, the results shown below can be achieved, much more simply and easily, using the minicalendar text framing and shading options and QuarkXPress 2017 and above.
The information below should only be used to maintain existing, pre-2018 diaries, or if you are not yet using QuarkXPress 2017.
The Show only on Current Day minicalendar modifier, denoted by :cd, can be used to specify that only those dates corresponding to the current date(s) should be displayed (where each date is determined to be current or not, based on the current day settings of the Minicalendar Options).
This option is usually used to display a box, oval, circle, frame, ..., to highlight the current day(s), as shown in the examples below :
To obtain the result shown above (white text on a black oval), you would use 2 minicalendar textboxes, one on top of the other (the 2 textboxes are shown side-by-side, below, to make the picture more legible).
The minicalendar textbox on the right [1mc+00:cd-alt1] uses a minicalendar token that uses a Show only on Current Day Minicalendar Modifier and the indication that on those dates the dates should be displayed using the following alternate font formatting (the -alt2 modifier is also available) :
Note that the numbers corresponding to the dates of current days are replaced by a constant character in a symbol-like font, on every current day date, regardless of it value. This is quite typical of the use of the Show only on Current Day Minicalendar Modifier.