lol, i love this thread. I have to deal with this all the time. semi-casual has to do with what that group already considers casual! If casual is jeans and tank tops then you just need to step it up a bit. Nice dressy jeans and a nice flattering top with any shoes will probably do. Accessories seem very suited to this category. On the other hand, if causal is dockers and polo for men, slacks, skirt, long shorts , and blouses for women, then you would need to step that up a bit too. Try a nice ‘do’ for your hair as well as a nice top that isn’t too revealing and some slacks or a modest skirt. In this sort of place I wouldn’t consider sandals, closed toed but no need for heals.
LOL, attire can be so complicated. I envy men. All it really changes for them is button up or polo? slacks or jeans? tucked in or not? dark or light? LOL, how wonderful that must be!