.previous {
position: fixed;
    bottom:6vh;
    right:2.5vw; 
    width:5vw;
    height: 4vh;
}

.next {
position: fixed;
    bottom:12vh;
    right: -0.5vw; 
    width: 4vw;
    height: 4vh;
}
.previousbut {
    position: fixed;
    bottom:4vh;
    right:2vw; 
    width:4vw;
    height: 4vh;
  }
    .nextbut {
    position: fixed;
    bottom:12vh;
    right: -0.5vw; 
    width: 3vw;
    height: 4vh;
  }
   a.previous img, a.next img {
        width: 90%; 
        max-width: 20vw; }
a.previousbut img, a.nextbut img {
  width: 90%;
  max-width: 20vw;  }
  @media (max-width: 768px){
  a.previous img,
  a.previousbut img {
    position: fixed;
        bottom:5vh;
        right:7vw; 
        width:9vw;
        height: 6vh;
    } 
    a.next img,
    a.nextbut img  {
    position: fixed;
        bottom:12vh;
        right: 1vw; 
        width: 6vw;
        height: 6vh;
  }
}

@media (max-width: 480px) {
      a.previous img,
      a.previousbut img {
          position: fixed;
              bottom:5vh;
              right:8vw; 
              width:9vw;
              height: 6vh;
          }
          a.next img,
          a.nextbut img  {
          position: fixed;
              bottom:12vh;
              right: 3vw; 
              width: 7vw;
              height: 6vh;
          }
  }