I've set up a very simple conditional format on a numeric column, with numbers less than zero colored red, and numbers greater than zero colored green. Now, if I also want to make the column bold when an additional condition is true (1st of the month, derived from a formula).

=DAY($C130)=1

But it seems that only one of the conditions can be met, and only one conditional format applied. Or am I doing something wrong?

Is it necessary to use four conditions for something like this? Red/non-bold, red/bold, green/non-bold, green/bold? That would quickly become onerous if you wanted to add additional formatting like borders, italics, etc.