Girls by their very nature are supposed to be delicate, feminine and very tender. It is this very aspect of their looks when contrasted with casual wear which is often rugged that makes a very striking picture. That is why girls in denim shorts look so hot, as this is the very picture of contrast. There is the simple but markedly masculine looking pair of shorts of made up of denim that is on the delicate legs of a girl.
Many men do not know this, but they often tend to find women or girls wearing casual clothing very attractive, even as they cannot fathom the reason why. In the olden days this was not something that you got to see a lot; that is women in casual clothes. You could see girls in different types of frocks and gowns and this was a pretty sight but not the same visual impact that a pretty girl or women in casual clothes has.
But as the times advanced and women started participating in most activities, slowly casual clothes have become the norm. But even today there is a certain part in the genealogical makeup of men that makes them gawk at the contrast that a girlish girl makes in simple and rugged casual clothes.
The thing that women need to remember while wearing casual clothes is to ensure that they adapt the clothing to their specific features. Like a girl wearing faded jeans would be better of teaming it with a cute T shirt than with a rugged shirt unless she is really petite. The same way a very casual pair of shorts can be made to look really striking by putting it together with a feminine lace or flowery top. Girls in casual clothing is all about the contrasts.