NotSpaghetti
As a girl, women (and some girls) wore a "head covering" of some sort in church. In those days yes, women wore a black dress and veil to meet the Pope.
It was about modesty.
I think it was early 1900s that it came into Canon law but was revised out in the 1980s.
I think your arms (shoulders at least) and your knees have to still be covered.
(Again - modesty)
I think lots of catholics will wear a mantilla or veil out of choice.
It's mainly a cultural thing- when younger I wore a black mantilla, which is a Spanish term, not for any holy reason but I thought it was cool.
The tradition all but died out following Vatican II, but women can still choose to wear one, or a hat. Men wearing hats or hoodies in church is frowned on though. It's all about respect in the end.
Recently in my church there was a young lady wearing a white mantilla paired with very short shorts. It seemed inappropriate to me but there you go...
The rubric now is cover arms and legs above the knee, but no one 'enforces' it except in some countries I've been to.
Being in church is much better than staying away, whatever you're wearing...