This is a relatively casual dress code, but you should have dressed up. Do not wear everyday clothes! 
     
Men can choose a light suit or a nice suit trousers and shirt, possibly with a jacket. Here you can also wear loafers (shoes without laces), folded suit trousers or nice shorts.
      
For ladies the dresses can reach to the knees / hips, or you can choose a nice trouser suit. You can also wear a long dress. All colors allowed. The style may well be summery.