.galeria {
    height: calc( 300px + 3em);
    width: 400px;
    margin:1em auto;
    display: flex;
    flex-wrap: wrap;
    justify-content: space-around;
    position: relative;  
  }
  
  
  
  .galeria img {
    position: absolute;
    top: 0;
    left: 0;
    opacity: 0;
    transition: opacity 3s;
    width: 400px;
      height: 300px;
  }
  
  .galeria input[type=radio] {
    position: relative;
    bottom: calc(-300px - 1.5em);
    left: .5em;
  }
  
  .galeria input[type=radio]:nth-of-type(1):checked ~ img:nth-of-type(1) {
    opacity: 1;
  }
  
  .galeria input[type=radio]:nth-of-type(2):checked ~ img:nth-of-type(2) {
    opacity: 1;
  }
  
  .galeria input[type=radio]:nth-of-type(3):checked ~ img:nth-of-type(3) {
    opacity: 1;
  }
  
  .galeria input[type=radio]:nth-of-type(4):checked ~ img:nth-of-type(4) {
    opacity: 1;
  }