#back-to-top-btn{
    display:none;
    position:fixed;
    bottom:100px;
    right:15px;
    font-size:26px;
    width:50px;
    height:50px;
    background-color: #ffff;
    color:#333;
    cursor:pointer;
    outline:none;
    border:3px solid #333;
    border-radius: 50%;
    transition: duration 0.2s;
    transition-timing-function: ease-in-out;
    transition-property:background-color,color;
    z-index:2;

}

#back-to-top-btn:hover, #back-to-top-btn:focus{
    background-color: #333;
    color:#ffff;  
}

@media(max-width: 992px) {
    .container { padding: 20px 100px; }
    #back-to-top-btn { font-size: 22px; width: 40px; height: 40px; bottom: 15px; right: 15px; }
    #back-to-top-btn:hover, #back-to-top-btn:focus{
      background-color: #ffff;
      color:#333;  
  }
  }
  @media(max-width:768px) {
    body { font-size: 16px; }
    .container { padding: 10px 50px; }
    h1 { font-size: 26px; }
    h2 { font-size: 22px; }
    hr { margin: 30px 0; }
    #back-to-top-btn { font-size: 18px; width: 45px; height: 45px; bottom: 90px; right: 17px; }

    #back-to-top-btn:hover, #back-to-top-btn:focus{
      background-color: #ffff;
      color:#333;  
  }
  }