html {
    box-sizing: border-box;
    -webkit-font-smoothing: subpixel-antialiased;
    -moz-osx-font-smoothing: auto;
  }
  
  *,
  ::before,
  ::after {
    box-sizing: inherit;
    margin: 0;
  }
  

  
  /* ============================
  mainsection
  ============================ */

  .back-to-top{
    display:none;
    position:fixed;
    right:5%;
    bottom:5%;
    color:#fff;
    padding:2rem;
    border-radius:50%;
    display:inline-block;
    text-decoration:none;

  }
  .back-to-top::before{
    content:'';
    position: absolute;
    top: 50%;
    left: 50%;
    transform: translate(-50%, -50%);
    display:inline-block;
    width:70px;
    height:70px;
    background-color:rgba(0,188,134, 0.6);
    border-radius:50%;
    z-index:-1;
  }