If we think of the style of trousers, obviously we have a few options to choose from, however, it might be helpful for you if I share with you about one of my favourite styles of trousers which is quite versatile and elegant as well.
Actually, it is a classic style of trousers which is emerged from the elite soldiers (who call themselves Gurkha) of the kingdom of Gurkha in Nepal; who began to wear it as their uniform trousers, after that, it gets familiar in the British military tradition when the Gurkha's served in the British army, then civilians get inspired and began to wear it with their everyday outfits.
Indeed, the Gurkha trouser is one of my favourite styles of trousers which is visually captivating, and this style of trouser could be combined with many of my outfits even casual; however, it will maintain the formality.
Relatively, the distinguishes of Gurkha trousers is typically a high-raised, cummerbund style waistband with buckles on each side of the trousers which would help to fasten the trouser and as always with double-pleats on the front, which I perceive the daintiness of the trousers.
As I said earlier it is easy to pair with your blazer, safari jacket, and sport coat, also you could have it as your suit trousers as well, whether it could be formal (business attire), semi-formal, business casual or even casual, it absolutely creates a flamboyant look.
Therefore, for casual I would like to wear linen, cotton, and seersucker Gurkha trousers; especially for summer you could have this style for your shots as well, of courses you could wear it with a polo t-shirt, a linen band collar or camp collar shirt and finished with a pair of loafers (penny, tassel, and Belgian loafers) and espadrilles.
However, for trousers, I would prefer loafers and Adelaide Oxford shoes and most importantly it is not an appropriate style of trousers for your black-tie, white-tie attire, rather it predominantly considers to wear with business attire. Hence, literally, I imply having a pair of Gurkha trousers in your wardrobe.