.top_btn{
  width: 55px;
  height: 55px;
  border-radius: 50%;
  background-color: #012255;
  display: flex;
  justify-content: center;
  align-items: center;
  position: fixed;
  right: 30px;
  bottom: 430px;
  z-index: 99;
  opacity: 0;
}
.top_btn i{
  font-size: 20px;
  color: #ffffff;
}

/* mobile */
@media screen and (max-width: 767px){ 
  .top_btn{
    width: 40px;
    height: 40px;
    bottom: 300px;
  }
  .top_btn i{
    font-size: 15px;
  }
}
  
/* tablet */
@media screen and (min-width: 768px) and (max-width: 1024px){
  .top_btn{
    width: 50px;
    height: 50px;
    bottom: 300px;
  }
  .top_btn i{
    font-size: 17px;
  }
}