It is actually pretty simple, something a bit more dressy than every day cloths. Some things that are not acceptable are Jeans, t-shirts and flips flops.
There is also a difference during day and night,
During the day you can wear a cute sun dress or a long dress, also linen pants or a skirt would be fabulous.
If is a night event you can go a bit more dressy such as a wrap dress, and white cotton pants
I hope this helps you!