.parent{margin:10px;padding:10px;background-color:#eee;border:1px solid #ccc}.parent div{margin:10px;padding:10px;width:200px;height:50px;font-size:16px;color:white;background-color:#00a}.parent1 :is(.child1,.child3){background-color:#0a0}.parent2:is(.child1,.child3){background-color:#0a0}