#mybtn {
    display: inline-block;
    background-color: #9BBE3D;
    width: 50px;
    height: 50px;
    text-align: center;
    border-radius: 15px;
    position: fixed;
    bottom: 0px;
    left: 0px;
    transition: background-color .3s,opacity .5s, visibility .5s;
    opacity: 0;
    visibility: hidden;
    z-index: 1000;
  }
  #mybtn::after {
    content: "\f077";
    font-family: FontAwesome;
    font-weight: normal;
    font-style: normal;
    font-size: 2em;
    line-height: 50px;
    color: #fff;
  }
  #mybtn:hover {
    cursor: pointer;
    background-color: #4285F4;
  }
  #mybtn:active {
    background-color: #555;
  }
  #mybtn.show {
    opacity: 1;
    visibility: visible;
  }
  

  @media (min-width: 500px) {

    #mybtn {
      margin: 17px;
    }
  }