CSS animation move didn't work

Question

I wanted to make an image of arrow moving so that readers know they can scroll down to read more content. I tried to do that with the animation in CSS but it didn't work.

section.scrollDownContainer {
  width: 100%;
  position: absolute;
  top: 65px;
}

section.scrollDownContainer img {
  display: block;
  box-shadow: 5px 5px 5px #333333;
  margin: auto;
  -webkit-animation: arrowmove 0.5s forwards;
  -moz-animation: arrowmove 0.5s forwards;
  -ms-animation: arrowmove 0.5s forwards;
  -o-animation: arrowmove 0.5s forwards;
  animation: arrowmove 0.5s forwards;
}

@-webkit-keyframes arrowmove {
  0% {
    left: 0px;
    top: 0px;
  }
  50% {
    left: 0px;
    top: 50px;
  }
  100% {
    left: 0px;
    top: 0px;
  }
}

@-moz-keyframes arrowmove {
  0% {
    left: 0px;
    top: 0px;
  }
  50% {
    left: 0px;
    top: 50px;
  }
  100% {
    left: 0px;
    top: 0px;
  }
}

@-ms-keyframes arrowmove {
  0% {
    left: 0px;
    top: 0px;
  }
  50% {
    left: 0px;
    top: 50px;
  }
  100% {
    left: 0px;
    top: 0px;
  }
}

@-o-keyframes arrowmove {
  0% {
    left: 0px;
    top: 0px;
  }
  50% {
    left: 0px;
    top: 50px;
  }
  100% {
    left: 0px;
    top: 0px;
  }
}

@keyframes arrowmove {
  0% {
    left: 0px;
    top: 0px;
  }
  50% {
    left: 0px;
    top: 50px;
  }
  100% {
    left: 0px;
    top: 0px;
  }
}

<section class="scrollDownContainer">
  <img src="./image/arrow.png">
</section>

Can anyone tell me why? Thank you.

Answer 1

You can use transform: translateY(...) in keyframes

section.scrollDownContainer {
  width: 100%;
  position: absolute;
  top: 65px;
}

section.scrollDownContainer img {
  display: block;
  margin: auto;
  animation: arrowmove 0.5s infinite;
}

@keyframes arrowmove {
  0% {
    transform: translateY(0%);
  }
  50% {
    transform: translateY(50%);
  }
  100% {
    transform: translateY(0%);
  }
}

<section class="scrollDownContainer">
  <img src="https://upload.wikimedia.org/wikipedia/en/f/f1/Down_Arrow_Icon.png" width="50px" height="50px">
</section>

Answer 2

The left: and top: properties of the animation will have no effect on your image because the image CSS does not contain a position property.

Add position: relative; or position: absolute; to the CSS for the image...

section.scrollDownContainer img {
  position: relative; /* <------------------- added */
  display: block;
  box-shadow: 5px 5px 5px #333333;
  margin: auto;
  -webkit-animation: arrowmove 0.5s forwards;
  -moz-animation: arrowmove 0.5s forwards;
  -ms-animation: arrowmove 0.5s forwards;
  -o-animation: arrowmove 0.5s forwards;
  animation: arrowmove 0.5s forwards;
}

The animation should then function.

Using left:, right:, top:, or bottom: in CSS requires the element to also have a position property.