.jia {
  background: url(../imgs/intro/jia.png) no-repeat center center;
  width: 24px; 
  height: 24px;
  cursor: pointer;  
  border: none;
  float: right;
}

.jian {
  background: url(../imgs/intro/jian.png) no-repeat center center;
  width: 24px; 
  height: 24px;
  cursor: pointer; 
  border: none;  
  float: right; 
}