First point: the English word 'elegant' is not always equivalent to the Spanish 'elegante'. When talking about clothes, 'smart' is the opposite of 'casual'. A man dressed casually might be wearing jeans and t-shirt; a man dressed smartly would be wearing a suit, a tie, and a shirt with a collar. Smart clothes ( British English) are the type of clothes you might wear for work. If you need to dress smartly for your job, you might wear a tailored skirt or trousers with a nice blouse and jacket. These clothes are smart, but they are not necessarily elegant. Elegant is something else: it suggests class, refinement, and stylishness. For someone to look elegant, they need more than smart clothes. An elegant person is likely to be tall and slim; they are also likely to have good posture and poise. Here's an example of 'elegant': https://pleasurephotoroom.wordpress.com/2013/01/15/fashion-photo-john-french-50s/

Thank you for your answer.

We can use "smart" to describe office clothes and business attire, "elegant" can be used to describe things like ball gowns, evening wear like a dinner suit or tuxedo or extraordinary designer clothes.