More vocabulary differences.
I remember my baffled bewilderment when I first came across a reference in some American novel to a character wearing 'dress shirt'. The context of the story did not suggest a dinner jacket, or tuxedo. This is because, in the UK, what we term a 'dress shirt' is what is what accompanies a tuxedo, or a white tie outfit.
A normal shirt, a collared shirt that one can wear with a tie, or open necked, is simply called 'a shirt'. We don't use the term 'dress shirt' (i.e. a proper collared shirt, a button up shirt) for something that is the standard.
However, what
@Apple fanboy means by 'smart trousers' are what used to be called 'slacks', that is, proper, well cut, sort of formal trousers, the sort that can be worn with a sports jacket, as well as with proper brogues, or shoes, and a proper buttoned up, collared shirt.