How to make the animation smooth?

Question

I am trying to create a pre-loader which changer its height, width, border-radius and background color.

The animation works, but it has a pause between the changes. How to make the animation smoother?

The fiddle: https://jsfiddle.net/Altair827/ww077qby/4/

#preloader {
  margin-left: 300px;
  margin-top: 200px;
  height: 20px;
  width: 20px;
  border-radius: 10px;
  background-color: violet;
  -webkit-animation-name: colorIt;
          animation-name: colorIt;
  -webkit-animation-duration: 3s;
          animation-duration: 3s;
  -webkit-animation-fill-mode: both;
          animation-fill-mode: both;
}

@-webkit-keyframes colorIt {
  from {
    background-color: violet;
  }
  to 20%,40%,60%,80%,90%,99% {
    
  }
  20% {
    background-color: indigo;
    height: 40px;
    width: 40px;
    border-radius: 20px;
  }
  40% {
    background-color: blue;
    height: 50px;
    width: 50px;
    border-radius: 25px;
  }
  60% {
    background-color: green;
    height: 60px;
    width: 60px;
    border-radius: 30px;
  }
  80% {
    background-color: yellow;
    height: 70px;
    width: 70px;
    border-radius: 35px;
  }
  90% {
    background-color: orange;
    height: 80px;
    width: 80px;
    border-radius: 40px;
  }
  99% {
    background-color: red;
    height: 20px;
    width: 20px;
    border-radius: 10px;
  }
}

@keyframes colorIt {
  from {
    background-color: violet;
  }
  to 20%,40%,60%,80%,90%,99% {
    
  }
  20% {
    background-color: indigo;
    height: 40px;
    width: 40px;
    border-radius: 20px;
  }
  40% {
    background-color: blue;
    height: 50px;
    width: 50px;
    border-radius: 25px;
  }
  60% {
    background-color: green;
    height: 60px;
    width: 60px;
    border-radius: 30px;
  }
  80% {
    background-color: yellow;
    height: 70px;
    width: 70px;
    border-radius: 35px;
  }
  90% {
    background-color: orange;
    height: 80px;
    width: 80px;
    border-radius: 40px;
  }
  99% {
    background-color: red;
    height: 20px;
    width: 20px;
    border-radius: 10px;
  }
}

<div id="preloader"></div>

Answer 1

You should change yout timing function:

animation-timing-function: linear;

You could also use a shortland:

/* @keyframes duration | timing-function | delay | name */
animation: 3s linear .1s colorIt;

Answer 2

The default easing for CSS animations is ease. Set it to linear and there should be no pauses:

animation-timing-function: linear;

#preloader {
  margin-left: 300px;
  margin-top: 200px;
  height: 20px;
  width: 20px;
  border-radius: 10px;
  background-color: violet;
  -webkit-animation-name: colorIt;
  animation-name: colorIt;
  -webkit-animation-duration: 3s;
  animation-duration: 3s;
  -webkit-animation-fill-mode: both;
  animation-fill-mode: both;
  -webkit-animation-timing-function: linear;
  animation-timing-function: linear;
}
@-webkit-keyframes colorIt {
  from {
    background-color: violet;
  }
  to 20%,
  40%,
  60%,
  80%,
  90%,
  99% {} 20% {
    background-color: indigo;
    height: 40px;
    width: 40px;
    border-radius: 20px;
  }
  40% {
    background-color: blue;
    height: 50px;
    width: 50px;
    border-radius: 25px;
  }
  60% {
    background-color: green;
    height: 60px;
    width: 60px;
    border-radius: 30px;
  }
  80% {
    background-color: yellow;
    height: 70px;
    width: 70px;
    border-radius: 35px;
  }
  90% {
    background-color: orange;
    height: 80px;
    width: 80px;
    border-radius: 40px;
  }
  99% {
    background-color: red;
    height: 20px;
    width: 20px;
    border-radius: 10px;
  }
}
@keyframes colorIt {
  from {
    background-color: violet;
  }
  to 20%,
  40%,
  60%,
  80%,
  90%,
  99% {} 20% {
    background-color: indigo;
    height: 40px;
    width: 40px;
    border-radius: 20px;
  }
  40% {
    background-color: blue;
    height: 50px;
    width: 50px;
    border-radius: 25px;
  }
  60% {
    background-color: green;
    height: 60px;
    width: 60px;
    border-radius: 30px;
  }
  80% {
    background-color: yellow;
    height: 70px;
    width: 70px;
    border-radius: 35px;
  }
  90% {
    background-color: orange;
    height: 80px;
    width: 80px;
    border-radius: 40px;
  }
  99% {
    background-color: red;
    height: 20px;
    width: 20px;
    border-radius: 10px;
  }
}

<div id="preloader"></div>

Answer 3

You want to set your animation curve to be linear:

-webkit-animation-timing-function: linear; /* Chrome, Safari, Opera */
animation-timing-function: linear;

This will ensure that your animation runs smoothly:jsfiddle