What Would Be Truly Stylish Causal Attire?

I have seen quite a few posts under a number of topics that lament the lack of clear rules, principles, and examples of truly stylish causal dress. Why don't we try to fix that?

By ‘causal’ here I do not mean what you wear to clean out the garage, but merely an outfit that contains neither suit, tie, blazer (nor DJ). This is something that might be used in informal but important settings either in business, travel or, say, romance. (Now by 'stylish' here I do not mean merely appropriate. Rather, I mean something more than that, namely, positively aesthetically pleasing. What are some causal such looks that really look good.)

There surely must be some paradigmatic examples of such attire that are still truly stylish. Let's discuss them (?) Perhaps we can use such examples to eventually come up with rules and principles of truly stylish causal dress (?)