/* -------------------------------------------------------------------------
   begin Scroll Down Button
 * ------------------------------------------------------------------------- */
button.scroll_down {
  position: absolute;
  margin-left: auto;
  margin-right: auto;
  left: 0;
  right: 0;
  height: 50px;
  width: 30px;
  bottom: 60px;
  background-color: transparent;
  border: 2px solid white;
  border-radius: 20px;
  cursor: pointer;
  outline: none;
  z-index: 90;
}

button.scroll_down:before {
  position: absolute;
  top: 10px;
  left: 50%;
  content: '';
  width: 6px;
  height: 6px;
  margin-left: -3px;
  background-color: #fff;
  border-radius: 100%;
  -webkit-animation: scroll_down_btn-animation 2s infinite;
  animation: scroll_down_btn-animation 2s infinite;
  box-sizing: border-box;
}

@keyframes scroll_down_btn-animation {
  0% {
    -webkit-transform: translate(0, 0);
            transform: translate(0, 0);
    opacity: 0;
  }
  40% {
    opacity: 1;
  }
  80% {
    -webkit-transform: translate(0, 20px);
            transform: translate(0, 20px);
    opacity: 0;
  }
  100% {
    opacity: 0;
  }
}
@-webkit-keyframes scroll_down_btn-animation {
  0% {
    -webkit-transform: translate(0, 0);
    transform: translate(0, 0);
    opacity: 0;
  }
  40% {
    opacity: 1;
  }
  80% {
    -webkit-transform: translate(0, 20px);
    transform: translate(0, 20px);
    opacity: 0;
  }
  100% {
    opacity: 0;
  }
}
/* -------------------------------------------------------------------------
   end Scroll Down Button 
 * ------------------------------------------------------------------------- */
/* ## Test ## */
.block {
  height: 2000px;
  border-top: 1px solid red;
}