Are there any direct declarations from a Pope or the Holy See that says explicitly that women should not wear pants? I have a hard time refuting the pro-pants argument that Rome never mentioned it specifically. I know Padre Pio and Cardinal Siri’s rules, but I was looking for a statement with binding authority on the matter.

Not that I know of. In the western (Christianized) world, pants came to be associated with men while women continued to wear robes. After all, Jesus and the disciples did not wear pants. Both sexes wore robes of some sort, but there was always a way to distinguish male from female clothing. Mary and Joseph did not swap out each other’s clothing!

I am simple making an observation, not expressing an opinion.  In the image below Our Lord has a beard and his head is uncovered.  Our Lady is wearing a veil.  One is obviously male and one obviously female.  I discern no distinguishing difference in their clothing.

Women only (widely) began wearing pants in the 1960s, and Cardinal Siri spoke out about it, in great detail.  The reason why Rome didn't speak up is because they were all battling it out over V2, which began in 1963. 

People who are arguing that it's ok because "the Church hasn't said no" are obviously ignoring Our Lady of Fatima's warnings from 1917 about "certain fashions will be introduced".  And then they are also ignoring Cardinal Siri.  They won't be able to ignore the Judgement day, that's for sure.

Will you please supply a link to Cardinal Siri's position on this?

Will you please supply a link to Cardinal Siri's position on this?

I don't have it.  It was posted on here long ago.  Use search.

I believe the meaning behind this is that a male should not aim to dress as if he were a woman and visa versa.... As for individual pieces of clothing, it depends on why you wear them....  Wearing pants as the norm instead of skirts is certainly one of the first steps in that direction.

Your thoughts are reducing the matter to 'intention' which is subjective.  But Scripture does not include allowances for intention; it says "shall not".  Neither does Cardinal Siri make allowances for "intention".  And the age-old loophole that "you need to wear pants if you're riding a horse or doing farm work."  Well, in the 1800s, it was considered unladylike for women to ride horses, as a man does.  And plenty of women have done farm work (and even hiked and swam) in dresses.  Intention is not part of the equation.

"Shalt not be clothed with man's apparel..."  The meaning is not directed at 'pants' per say as a piece of individual clothing but in the broader sense of "dressing as a man" in masculine attire.

Pants have been man's attire since the day they were invented (600s BC).  So that's 2,600 years.
Women have only worn pants since 1960 -- 60 years.
2,600 years vs 60 years.  Do the math.

My intent to put on trousers to back a horse, is not to attire myself as a man, but to ensure that my clothing doesn't cause me to become ensnared in the saddle and break my neck. Gone are the days when you can pick up a side-saddle for cheap. And this is where common sense comes into play. 

The exception proves the rule.  If you want to argue that in SPECIFIC circuмstances, it's ok to wear pants, fine.  This is about 1% of ones' time.  99% of the time, you're not working with horses.  ...Unless you're a horse worker, which again, is only about 1% of the population (probably less).  

99% of the time, the 99% of women have no need to wear pants.

The last time I checked the calendar it was 2025. You cannot apply the norms of the 1800's to the here and now.

  Morals don't change.  The 10 commandments don't change.  God doesn't change.  Your argument is Modernist.

That is YOU dictating.

No, it's God dictating.  It's Scripture teaching.  It's Our Lady of Fatima's warnings.  It's Cardinal Siri preaching.  ...I'm just explaining it to you.

Regardless of when they were introduced, today, pants are considered both male and female apparel.

  A godless society does not get to re-write God's rules.  Catholics don't live their lives based on "what is considered normal" by anti-catholic people.  Can't believe you're making this argument.

As such, although we should be encouraging a more feminine way of dressing, making 'pants' a cardinal sin in itself, and reaching for your stones, is turning Catholicism into a pharisaical religion.

If women wore pants in the 1950s (or anytime PRIOR to this), there would be shock and scandal.  Let that sink in.  

Your arguments are Modernist...that morals can change over time.  No, they can't.  Pants have always been men's attire.  From day 1.

My calendar also indicates it’s 2025, not 1825, 1525, 1025, 125, or 25. It’s certainly not the time of Moses, either.  Clothing customs change over time and between cultures.  What doesn’t change are the principles of God’s Word. Throughout time and across cultures, there have, until recently, different clothing for men and for women, whatever outward form they may take. Our Lord and Our Lady call for Catholics to wear clothing that is modest, suitable to one’s sex, suitable to one’s age, and to one’s state in life. Clothing, in addition to meeting these qualifications, must be practical for the activity of the wearer.
When Our Lady about “certain fashions,” she did not specify what they were or for which sex.  She did not limit the fashions to clothing, either. Could fashions not apply also to accessories, to hair styles, to the manner of carrying oneself? 
Within Christ-like and Mary-like appearance, there is wiggle room. Ask yourself, am I modest? Obviously male or female? Dressed in accord with my state in life? Dressed appropriately for my activity? For the climate?  Am I age appropriate? Are my clothes suited to my culture, or do I draw unnecessary attention to myself?  The same should be asked of my hair style, makeup, jewelry, accessories like hats, gloves, scarves, etc.
Whether some trads like it or not, there IS no standardized “Traditional Catholic Uniform” for all but religious orders and organized institutions like schools and certain clubs. Many uniforms are reserved for specific times, like during school hours, on the job, or to club meetings.

This ^^^